on board diagnostic ii obd ii obd 2

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This document is intended to help in the understanding of OBDII parameters, known as ‘PIDs’, and give them definition. It is intended to be only a basic, not a technical guide to scantool data. These PIDS are used by the OBDII system and by scantools that interact with the systems for diagnostics and system interrogation. PID stands for Parameter Identification, and in practice is rather cryptic. The scantool, luckily, takes this cryptic, bit and byte data shorthand and translates it for us, so it is more understandable.

Live Data Trigger Frame PID Unit Frame These are parameters specific to the scantool being used in this case, and are not OBDII standard PIDs. Fuel System 1 Status [Status 1 or Fuelsys1] Fuel System 2 Status [Status 2 or Fuelsys2] Returns either OL – for Open Loop, or CL – for Closed Loop Tells whether fueling is currently based on O2 Sensors and the oxygen content of the exhaust, [Closed Loop] or based on sensor inputs [Open Loop] due to conditions; logged faults, cold engine or wide open throttle, for instance.

Calculated Load Value [CLV or Load_PCT] Engine load is represented by a "Calculated load value" which refers to an indication of the current airflow divided by peak airflow, where peak airflow is corrected for altitude, if available. This definition provides a unitless number that is not engine specific, and provides the system with an indication of the percent engine capacity that is being used. (With wide open throttle as 100%).

Engine Coolant Temp [ECT] Current engine coolant temp as measured by the ECT [Engine Coolant Temp sensor]. Usually reported in Celsius degrees.

Short Term Fuel Trim-Bank 1 [STFT 1 or SHRTFT1] Short Term Fuel Trim-Bank 2 [STFT 2 or SHRTFT2] Immediate trim changes made to the fuel mapping in response to oxygen changes in the exhaust. Base fueling [injection] map is contained in the ECM, if changes are required, fuel is added or subtracted from the base. Shown in percent, positive percentage is ADDING fuel, negative percentage is SUBTRACTING fuel. Short term trims are lost at key off.

Long Term Fuel Trim- Bank 1 [LTFT 1 or LONGFT1] Long Term Fuel Trim- Bank 2 [LTFT 2 or LONGFT2] Long term changes made to the fuel mapping based on Short Term fueling corrections. Example: Short Term remaining at plus 6% for an extended period; Long Term Trim will increment by that percentage and Short Term will return to zero. Long Term Trims are maintained in non-volatile memory at key off, and therefore not lost.

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Engine RPM [RPM] I think this one is self explanatory.

Vehicle Speed Sensor [VSS] Returns current vehicle speed, usually shown in kph, but some scantools allow selecting kilometers or miles per hour.

Ignition Timing Advance #1 [Sparkadv] Shows current spark timing advance in degrees for cylinder #1. Most engines with knock retard systems can retard timing for individual cylinders, however.

Intake Air Temp [IAT] Returns current temperature of the air entering the induction system. Like ECT, usually reported in degrees Celsius, but some tools allow selecting scale.

Air Flow Rate from Mass Air Flow Sensor [MAF] Returns the ECM calculation of total air flow, based on MAF signal AND air temperature [IAT]. Most systems list this in grams per second, g/sec.

Absolute Throttle Position [TP or ABS_TP] Listed in percent, shows actual position of the throttle butterfly, as it is not directly connected to any cable or other driver input.

Bank 1 -- Sensor 2 Volts [O2S12] Bank 2 – Sensor 2 Volts [O2S22] Voltage output of downstream [second] Exhaust Oxygen sensor. Varies between .2v and .8v normally. Used mainly for monitoring exhaust catalyst function.

Bank 1 – Sensor 2 % [O2S12STFT] Bank 2 – Sensor 2 % [O2S22STFT] Returns an additional trim value to the ECM for extremely fine fueling corrections.

Not used except for later model years, 2006 and later. Generally not useful to the novice .

OBD Requirements OBD and OBD2 [OBDSUP] Returns information to define which OBD requirements the vehicle was designed to meet; i.e. which OBD system is onboard.

01h : OBD II (California ARB) 02h : OBD (Federal EPA) 03h : OBD and OBD II 04h : OBD I 05h : not intended to meet any requirements 06h : EOBD (Europe) 07h : EOBD and OBD II

08h : EOBD and OBD 09h : EOBD, OBD and OBD II 0Ah : JOBD 0Bh : JOBD and OBD 0Ch : JOBD and EOBD 0Dh : JOBD, EOBD, and OBD II 0Eh-FFh : Reserved by SAE J1979

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Now, upstream Oxygen Sensors are a little more confusing. Earlier cars use upstream units that are very similar to the downstream sensors, called zirconium dioxide sensors.

They are also referred to as ‘Heated Exhaust Gas Oxygen’ sensors, or HEGO sensors.

Their output signal is voltage just like the downstream; it swings from .2v to .8v about 15-18 times a minute normally. These were fitted to the AJ26 V8 and the first generation S-Type, both V6 and V8.

Beginning with the AJ27 4.0L V8 in 1999 and the AJ33 4.2L V8 in 2003, the upstream oxygen sensors operated differently. These are referred to as ‘wideband’ or ‘linear’ sensors. To add confusion, they are also called ‘Universal’ Heated Exhaust Gas Oxygen sensors, or UHEGO. The signal PID for these sensors is CURRENT, in milliamps or microamps as the case may be. ***Note: The six-cylinder AJ16 engines utilize a different, Titanium Dioxide Oxygen Sensor at all four positions, this is a very delicate five volt sensor that is beyond the scope of this paper.  Conventional [HEGO] Oxygen Sensors Bank 1 – Sensor 1 [O2S11] Bank 2 – Sensor 1 [O2S21] Voltage output of upstream [first] Exhaust Oxygen sensor. Varies between .2v and .8v normally. Used mainly for fueling control, air/fuel ratio and emissions monitoring.  Universal [UHEGO] Oxygen Sensors Bank 1 – Sensor 1 [WO2S11] Bank 2 – Sensor 1 [WO2S21] ECM monitors the current, positive or negative, needed to drive the operation of the sensor in response to the exhaust oxygen content, and reports that value.

Positive amps indicate a lean system and negative indicate a rich system.

Bank 1 – Sensor 1 Equivalence Ratio Bank 2 – Sensor 1 Equivalence Ratio This PID is of limited value to technicians, and has even less value to the novice.

This value is the commanded fuel to oxidizer ratio that the ECM wants to achieve. In essence ‘Equivalence Ratio’ is the reciprocal of the air/fuel ratio.

Revision 2 ©S. Petry Indianapolis, IN 8/24/2011

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OBDII and Emissions Testing

Are you up to speed on OBD II? You should be because starting in 2002, a number of states have announced plans to change their emissions testing programs over to OBD II. Instead of doing a tailpipe emissions check on a dynamometer, an OBD II check is a simple plug-in test that takes only seconds. What’s more, OBD II will detect emissions problems that might not cause a vehicle to fail a tailpipe test - which means emissions test failures under the OBD II test programs are expected to be significantly higher.

The second-generation self-diagnostic emissions software has been required on all new vehicles sold in this country since model year 1996, including all imports. OBD II is a powerful diagnostic tool that can give you insight into what’s actually happening within the engine control system.

Unlike earlier OBD systems that set a DTC when a sensor circuit shorts, opens or reads out of range, OBD II is primarily emissions-driven and will set codes anytime a vehicle’s emissions exceed the federal limit by 1.5 times.It also will set codes if there is a gross sensor failure, but some types of sensor problems won’t always trigger a code. Consequently, the Check Engine light on an OBD II-equipped vehicle may come on when there is no apparent driveability problem, or it may not come on even though a vehicle is experiencing a noticeable driveability problem.

The determining factor as to whether or not the Check Engine light comes on is usually the problem’s effect on emissions. In many instances, emissions can be held in check, despite a faulty sensor, by adjusting fuel trim. So as long as emissions can be kept below the limit, the OBD II system may have no reason to turn on the light.

CHECK ENGINE LIGHT The "Malfunction Indicator Lamp" (MIL), which may be labeled "Check Engine" or "Service Engine Soon" or a symbol of an engine with the word "Check" in the middle, is supposed to alert the driver when a problem occurs.

Depending on how the system is configured and the nature of the problem, the lamp may come on and go off, remain on continuously or flash - all of which can be very confusing to the motorist because he has no way of knowing what the light means. Is it a serious problem or not? If the engine seems to be running okay, the motorist may simply ignore the light. With OBD II, the Check Engine light will come on only for emissions-related failures. A separate warning light must be used for other non-emissions problems such as low oil pressure, charging system problems, etc.

If the light is on because of a misfire or a fuel delivery problem, and the problem does not recur after three drive cycles (under the same driving conditions), the Check Engine light may go out. Though you might think the vehicle has somehow healed itself, the intermittent problem may still be there waiting to trigger the light once again when conditions are right. Whether the light goes out or remains on, a code will be set and remain in the computer’s memory to help you diagnose the fault.

With some exceptions, the OBD II warning lamp will also go out if a problem does not recur after 40 drive cycles. A drive cycle means starting a cold engine and driving it long enough to reach operating temperature.

The diagnostic codes that are required by law on all OBD II systems are "generic" in the sense that all vehicle manufacturers use the same common code list and the same 16-pin diagnostic connector. Thus, a P0302 misfire code on a Nissan means the same thing on a Honda, Toyota or Mercedes-Benz. But each vehicle manufacturer also has the freedom to add their own "enhanced" codes to provide even more detailed information about various faults.

Enhanced codes also cover non-emission related failures that occur outside the engine control system. These include ABS codes, HVAC codes, air bag codes and other body and electrical codes.

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The second character in an OBD II will be a zero if it’s a generic code, or a "1" if it’s a dealer enhanced code (specific to that particular vehicle application).

The third character in the code identifies the system where the fault occurred. Numbers 1 and 2 are for fuel or air metering problems, 3 is for ignition problems or engine misfire, 4 is for auxiliary emission controls, 5 relates to idle speed control problems, 6 is for computer or output circuit faults, and 7 and 8 relate to transmission problems.

Codes can be accessed and cleared using an OBDII scan tool such as AutoTap. MISFIRE DETECTION If an emissions problem is being caused by engine misfire, the OBD II light will flash as the misfire is occurring.

But the light will not come on the first time a misfire problem is detected. It will come on only if the misfire continues during a second drive cycle and will set a P0300 series code.

A P0300 code would indicate a random misfire (probably due to a vacuum leak, open EGR valve, etc.). If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Causes here would be anything that might affect only a single cylinder such as a fouled spark plug, a bad coil in a coil-on-plug ignition system or distributorless ignition system with individual coils, a clogged or dead fuel injector, a leaky valve or head gasket.

The OBD II system detects a misfire on most vehicles by monitoring variations in the speed of the crankshaft through the crankshaft position sensor. A single misfire will cause a subtle change in the speed of the crank.

OBD II tracks each and every misfire, counting them up and averaging them over time to determine if the rate of misfire is abnormal and high enough to cause the vehicle to exceed the federal emissions limit. If this happens on two consecutive trips, the Check Engine light will come on and flash to alert the driver when the misfire problem is occurring.

Misfire detection is a continuous monitor, meaning it is active any time the engine is running. So too is the fuel system monitor that detects problems in fuel delivery and the air/fuel mixture, and something called the "comprehensive monitor" that looks for gross faults in the sensors and engine control systems. These monitors are always ready and do not require any special operating conditions.

Other OBD II monitors are only active during certain times. These are the "non-continuous" monitors and include the catalytic converter efficiency monitor, the evaporative system monitor that detects fuel vapor leaks in the fuel system, the EGR system monitors, the secondary air system monitor (if the vehicle has such a system), and the oxygen sensor monitors.On some 2000 and newer vehicles, OBD II also has a thermostat monitor to keep an eye on the operation of this key component. The thermostat monitor will be required on all vehicles by 2002. On some 2002 model-year vehicles, there also is a new PCV system monitor, which will be required on all vehicles by 2004.

The catalytic converter monitor keeps an eye on converter efficiency by comparing the outputs from the upstream and downstream oxygen sensors. If the converter is doing its job, there should be little unburned oxygen left in the exhaust as it exits the converter. This should cause the downstream O2 sensor to flatline at a relatively fixed voltage level near maximum output.

If the downstream O2 sensor reading is fluctuating from high to low like the front sensor, it means the converter is not functioning.The Check Engine light will come on if the difference in O2 sensor readings indicates hydrocarbon (HC) readings have increased to a level that is 1.5 times the federal limit. For 1996 and newer vehicles that meet federal Low Emission Vehicles (LEV) requirements, the limit allows only 0.225 grams per mile (gpm) of HC - which is almost nothing. Converter efficiency drops from 99 percent when it is new to around 96 percent after a few thousand miles. After that, any further drop in efficiency may be enough to turn on the Check Engine light. We’re talking about a very sensitive diagnostic monitor.

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The EVAP system monitor checks for fuel vapor leaks by performing either a pressure or vacuum test on the fuel system. For 1996 through 1999 vehicles, the federal standard allows leaks up to the equivalent of a hole .040 inches in diameter in a fuel vapor hose or filler cap. For 2000 and newer vehicles, the leakage rate has been reduced to the equivalent of a .020 in. diameter hole, which is almost invisible to the naked eye but can be detected by the OBD II system. Finding these kinds of leaks can be very challenging.

READINESS FLAGS An essential part of the OBD II system are the "readiness flags" that indicate when a particular monitor is active and has taken a look at the system it is supposed to keep watch over. The misfire detection, fuel system and continuous system monitors are active and ready all the time, but the non-continuous monitors require a certain series of operating conditions before they will set - and you can’t do a complete OBD II test unless all of the monitors are ready.

To set the converter monitor, for example, the vehicle may have to be driven a certain distance at a variety of different speeds. The requirements for the various monitors can vary considerably from one vehicle manufacturer to another, so there is no "universal" drive cycle that will guarantee all the monitors will be set and ready.

As a general rule, doing some stop-and-go driving around town at speeds up to about 30 mph followed by five to seven minutes of 55 mph plus highway speed driving will usually set most or all of the monitors (the converter and EVAP system readiness monitors are the hardest ones to set). So if you’re checking the OBD II system and find a particular monitor is not ready, it may be necessary to test drive the vehicle to set all the monitors.

The Environmental Protection Agency (EPA) realized this shortcoming in current generation OBD II systems.

So, when it created the rules for states that want to implement OBD II testing in place of tailpipe dyno testing, it allows up to two readiness flags to not be set prior to taking an OBD II test on 1996 to 2000 vehicles, and one readiness flag not to be set on 2001 and newer vehicles. You can use the AutoTap OBDII scantool to check that your readiness flags are set before having your vehicle emissions-tested. This can save you the aggrevation of being sent off to drive around and come back later.

Some import vehicles have known readiness issues. Many 1996-’98 Mitsubishi vehicles will have monitors that read "not ready" because setting the monitors requires very specific drive cycles (which can be found in their service information). Even so, these vehicles can be scanned for codes and the MIL light without regard to readiness status.On 1996 Subarus, turning the key off will clear all the readiness flags. The same thing happens on 1996 Volvo 850 Turbos. This means the vehicle has to be driven to reset all the readiness flags. On 1997 Toyota Tercel and Paseo models, the readiness flag for the EVAP monitor will never set, and no dealer fix is yet available. Other vehicles that often have a "not ready" condition for the EVAP and catalytic converter monitors include 1996-’98 Volvos, 1996-’98 Saabs, and 1996-’97 Nissan 2.0L 200SX models.

OBD II TEST An official OBD II emissions test consists of three parts: 1. An inspector checks to see if the MIL light comes on when the key is turned on. If the light does not come on, the vehicle fails the bulb check.

2. A scanner similar to AutoTap is plugged into the diagnostic link connector (DLC), and the system is checked for monitor readiness. If more than the allowed number of monitors are not ready, the vehicle is rejected and asked to come back later after it has been driven sufficiently to set the readiness flags. The scanner also checks the status of the MIL light (is it on or off?), and downloads any fault codes that may be present.If the MIL light is on and there are any OBD II codes present, the vehicle fails the test and must be repaired. The vehicle also fails if the DLC is missing, has been tampered with or fails to provide any data.

3. As a final system check, the scanner is used to command the MIL lamp on to verify it is taking commands from the onboard computer. If the OBD II light is on, or a vehicle has failed an OBD II

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emissions test, your first job is to verify the problem. That means plugging into the OBD II system, pulling out any stored codes and looking at any system data that might help you nail down what’s causing the problem. Long-term fuel trim data can provide some useful insight into what’s going on with the fuel mixture. If long-term fuel trim is at maximum, or you see a big difference in the numbers for the right and left banks of a V6 or V8 engine, it would tell you the engine control system is trying to compensate for a fuel mixture problem (possibly an air leak, dirty injectors, leaky EGR valve, etc.).

OBD II also provides "snap shot" or "freeze frame" data, which can help you identify and diagnose intermittent problems. When a fault occurs, OBD II logs a code and records all related sensor values at that moment for later analysis.

Once you’ve pinpointed the problem and hopefully replaced the faulty component, the final step is to verify that the repair solved the problem and that the OBD II light remains off. This will usually require a short test drive to reset all the readiness monitors and run the OBD II diagnostic checks.

OBD II TOOLS & EQUIPMENT You can’t work on OBD II systems without some type of OBD II-compliant scanner. The AutoTap OBDII Scan Tool is available in both PC/laptop versions and Palm PDA versions. The computing power and display of a PC or Palm gives AutoTap a much broader range of features than the older style hand-held scantools.

The OBDII Home Page http://www.obdii.com

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Bulletin TB-80010 May, 2009

INTERPRETING FUEL TRIM DATA

Gary Stamberger – Training Director Car-Sound/Magnaflow Performance Exhaust This month we take the discussion of Oxygen Sensors to yet another level. In recent discussions we talked about the role these sensors played in closed loop fuel control. What exactly does that mean, “Closed loop fuel control”, and what role does it play in maintaining a good working converter?

When a vehicle is started cold there is a warm up period which is referred to as, “Open loop”. It’s during this time period that the engine is polluting the most. Consequently, getting to closed loop fuel control is a top priority. The PCM has an internal clock that restarts on each start-up and it knows, based mainly on temperature, how long before all components are operating and it is ready to enter closed loop. To this end, many elements have been added to the systems. Oxygen sensors have built in heaters to speed the warm up process. The PCM can detect when the engine is taking too long to come up to temperature and will set a code P0125, “Insufficient temperature for closed loop fuel control” which typically means the thermostat is stuck open.

Once the conditions are met and the PCM gains fuel control the goal then becomes maintaining it. The oxygen sensor is referred to as a, “Voltage Generator” and reports the content of oxygen in the exhaust stream to the PCM ranging between 100mv (Millivolts) and 900mv. When the oxygen content is high, (Voltage is low, near 100mv) the PCM sees this as a lean condition and its response is to add fuel. When the sensor reports back that there is little oxygen in the exhaust stream (high voltage, near 900mv), a rich condition is sensed and the PCM pulls fuel away. A technician can monitor this data on a scan tool as, “Short Term Fuel Trim” or STFT. A positive percentage indicates the computer is adding fuel while a negative number says it is taking fuel away. If the PCM is in fuel control, monitoring the direct relationship between O2 and STFT scan data will confirm it.

The next step then is to look at Long Term Fuel Trim (LTFT) percentages. These numbers give us a history of what the PCM has been doing with fuel trim over the long haul. As with STFT, positive percentages tell us the tendency is to be adding fuel (compensating for a lean condition) while negative numbers indicate the PCM is pulling fuel back, (Overcoming a rich condition). If either of these conditions exists for a prolonged period of time and the LTFT percentages exceed the PCM’s parameters a fuel trim code will set (P0170-P0175) and Check Engine light illuminated. The example below shows us that although the PCM appears to be in fuel control there is evidence that it has been adding fuel over time.

Our concern when looking at fuel trim is what it may be telling us about engine efficiency and whether the computer has been compensating for other fuel related problems. If the engine has been over-fueling the question is…WHY? A leaking fuel injector, fuel pressure regulator, lazy O2, or bad Mass Air Flow (MAF) would be some of the considerations. The same issue exists if it’s too lean. Here an air leak, clogged injectors or fuel filter, or miscalculated air flow could be the cause. Any Fuel Trim condition that persists will eventually take its toll on the catalytic converter and must be addressed by the repair technician before installing a new one.

Cleaning up the environment…one converter at a time

Gary

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OBD II Code Diagnosis Part III

Bulletin TB-80035 September, 2011

Gary Stamberger – Training Director Magnaflow Exhaust Products In the first part of this OBD II Code Diagnosis series I stated that we would discuss the principles of OBD II codes and breakdown each character that defines them. For a generic discussion of OBD I’ll refer you to TB-80016 and 80017. We archive all of our bulletins and they can be found on our website at www.maganaflow.com. Look for Tech Bulletins under Tech Support. For this series I would like to stay on a more specific path.

In our first two parts we took a very common Ford EGR code and broke down the diagnosis. I chose this code not only for its commonality but also because this EGR system uses several components, each one playing a major role in the vehicles ability to reduce NOx. Although the PCM has the ability to set several different and distinct codes for each component (9 generic and 10 specific) the interrelation of the components cannot be ignored. As we saw in our example, one of the possible causes for the P0401 code was mechanical and had nothing to do with the malfunction of any one component.

Another common issue in Code Diagnostics sometimes overlooked is that of retrieving codes in both OBD II Generic and Enhanced or Manufacture Specific mode. Depending on the tool being used, the enhanced option may not be available (i.e. Code Reader only).

Using generic mode requires less input therefore is faster and in most cases will get the technician to where he wants to be. The downside is that it is a generic code and therefore in many cases the repair information will not be specific to that vehicle.

The obvious upside then to using Enhanced Mode, is that the diagnostic information will be specific to that vehicle or at least that manufacturer. The description and operation will give you a better idea of what the PCM is looking for and the subsequent testing should lead you to the proper diagnosis the first time.

Example: 2005 Altima, 2.5L with an illuminated MIL. The OBD II code was P0140, O2 Circuit B1S2 No Activity Detected. A quick glance at the data stream showed that under the proper test conditions the sensor displayed activity. At this point we might determine that it is an intermittent problem, clear the code and send the customer on their way. However a look at Enhanced codes revealed a P1147, O2 B1S2 Maximum Voltage not Obtained. A closer look at data stream showed that the sensor was not reaching a specific maximum voltage of .78v. This specific information was not available when processing the P0140 code.

The key to any diagnostic situation is to always follow a pattern for each problem we face and code diagnostics is no different. Yes… each manufacture has common problems and knowing where to find that information is valuable but sometimes even the “silver bullet” can be a dud! Whether it is a no start, misfire, won’t idle, MIL illuminated or any number of issues, having a plan is by far the best plan. “Shot Gun” diagnosis will on occasion allow us to hit the illusive homerun but more often than not we spend a whole day repairing a component only to go home with that empty feeling in our stomachs, knowing the same problem will reoccur in the morning.

Diagnostics is an art and getting good at it can be a great confidence booster, however these vehicles are changing constantly and there is no time to rest. As I say when closing all my classes: THE RULES ARE ALWAYS CHANGING TECHNOLOGY KEEPS MOVING FORWARD EDUCATION IS A CONTINUAL PROCESS

Cleaning up the environment…one converter at a time Gary

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ScanMaster-ELM

What is OBD-II? OBD-II stands for On-Board Diagnostics second (II) generation, a computer-based system built into all model year (MY) 1996 in USA and newer light-duty cars and trucks. OBD-II monitors the performance of some of the engines' major components, including individual emission controls. The system provides owners with an early warning of malfunctions by way of a dashboard "Check Engine" light (also known as a Malfunction Indicator Light or MIL, for short). By giving vehicle owners this early warning, OBD-II protects not only the environment but also consumers, identifying minor problems before they become major repair bills.

EOBD - European On-Board Diagnostic EOBD is a standard that is issued by the European Community. The main goal with the standard is to give the authorities a tool to control the exhaust emission from vehicles. The EOBD standard has been implemented in petrol cars throughout the European Union from 01.01.2001 (EU directive 98/96/EC). For LPG and Diesel vehicles the implementation of applicable regulations is scheduled to take place before 2005. The EOBD standard includes five different communication protocols: ISO 9141-2, ISO 14230-4(KWP2000), SAE J1850 VPW, SAE J1850 PWM and ISO 15765-4 CAN. If the car supports EOBD you have the possibilities to read out stored information from the ECU in the car, including: € € € € € €

Read fault codes Erase fault codes Read freeze frame data Get real-time data (displayed as numbers or graphs) Get monitoring results from oxygen sensors Get result from readiness test

To read out the information you require an OBD-II/EOBD diagnostic tool such as the ScanMaster software together with an approbiate interface for the connection between the cars diagnostic connector and the computer or notbook.

How do I know the OBD system is working correctly?

When you turn on the ignition, the "Service Engine Soon" or "Check Engine" light should flash briefly, indicating that the OBD system is ready to scan your vehicle for any malfunctions. After this brief flash, the light should stay off while you drive as long as no problems are detected. If so, you'll be glad to know that your vehicle is equipped with an early warning system that could save you time, money, and fuel in addition to helping protect the environment!

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ScanMaster-ELM

Which OBD-II protocol is supported by vehicle?

All cars and light trucks built for sale in the United States after 1996 are required to be OBDII compliant. The European Union adopted a similar law in 2000 for gasoline-powered vehicles, and in 2003 for cars with diesel engines.

An OBD-II compliant vehicle can use any of the five communication protocols: J1850 PWM and VPW, ISO9141, ISO14230 (also known as Keyword Protocol 2000), and more recently, CAN (ISO15765/SAE J2480). Car manufacturers were not allowed to use CAN until model year 2003.

As a general rule, you can determine which protocol your vehicle is using by looking at the pinout of the DLC:

The following table explains how to determine the protocol: Pin 2

Pin 14

Pin 15*

ISO 9141-2 K Line and J1850 Bus ISO/DIS 14230-4

CAN Low

ISO 9141-2 L Line and ISO/DIS 14230-4

must have -

-

must have

-

-

J1850 PWM

must have -

-

-

-

-

J1850 VPW

-

-

must have

-

-

may have

ISO9141/14230

-

must have -

-

must have -

J1850 Bus+

Pin 6

CAN High

Pin 7

Pin 10

Standard

CAN

The connector should have: Pin 4 - Chassis Ground, Pin 5 - Signal Ground, Pin 16 - Battery power

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ScanMaster-ELM

This means that: Protocol

The connector must have pins

PWM

2, 4 and/or 5, 10, and 16

VPW

2, 4 and/or 5, and 16, but not 10.

ISO

4 and/or 5, 7, and 16. Pin 15 *may or may not be present.

CAN

4 and/or 5, 6, 14 and 16

*For ISO communications, pin 15 (L-line) is not always required. Pin 15 was used on earlier ISO/KWP2000 cars to "wake-up" the ECU before communication could begin on pin 7 (KLine). Later cars tend to communicate using only pin 7 (K-Line).

Because of the different protocol a car might have it is recommended to use an interface which supports all protocols as all modern interfaces do.

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ScanMaster-ELM

Diagnostic Link Connector (DLC) Mapping Diagram Explanation The mapping diagram of DLC locations contains a divided instrument panel (IP) with numbered areas. Each numbered area represents specific sections of the IP where manufacturers may have located DLCs. This document briefly clarifies the numbered locations on the mapping diagram. We will use this mapping diagram to catalog manufacturer responses to the recent 208 letter requesting OBD DLC locations for 96MY and future vehicles. Areas 1-3 fall within the preferred DLC location while the remaining areas, 48, fall into the allowable DLC location according to EPA requirements. Areas 4-8 require that manufacturers label the vehicle in the preferred location to notify parties of the alternate connector location.

Preferred Location(s) Location #1: This location represents a DLC positioned on the underside of the IP directly

under the steering column (or approximately 150mm left or right of the steering column).

Visualizing the underside of an IP divided into three equal parts from inside the passenger compartment, this represents the center section.

Location #2: This location represents a DLC positioned on the underside of the IP between

the steering column and the drivers side passenger door. Visualizing the underside of an IP divided into three equal parts from inside the passenger compartment, this represents the left section.

Location #3: This location represents a DLC positioned on the underside of the IP between

the steering column and the center console. Visualizing the underside of an IP divided into three equal parts from inside the passenger compartment, this represents the right section.

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ScanMaster-ELM Allowable Location(s) Location #4: This location represents a DLC positioned on the upper part of the IP between the steering column and the center console (but not on the center console, see location #6).

Location #5: This location represents a DLC positioned on the upper part of the IP between the steering column and the driver side, passenger door.

Location #6: This location represents a DLC positioned on the vertical section of the center

console and left of the vehicle center line.

Location #7: This location represents a DLC positioned 300 mm right of the vehicle centerline either on the vertical section of the center console or on the passenger side of the vehicle.

Location #8: This location represents a DLC positioned on the horizontal section of the

center console either left or right of the vehicle center line. This does not include the horizontal section of the center console that extends into the rear passenger area (see location #9).

Location #9: This location, not shown, represents any DLC positioned in an area other than

those mentioned above (e.g., in the rear passenger area on the driver side armrest).

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ScanMaster-ELM

OBD-II Diagnostic Protocol The diagnostic protocol for OBD-II is SAE J1979. A diagnostic request or response message has a maximum of seven data bytes. The first byte following the header is the test mode. It is also called the service identifier (SID or PID). The following bytes vary depending on the specific test mode.

There are nine diagnostic test modes: Mode $01 – Request Current Powertrain Diagnostic Data - This service gives access to current emission-related data values, including analogue inputs and outputs, digital inputs and outputs and system status information.

Mode $02 – Request Powertrain Freeze Frame Data - This service gives access to current emission-related data values in a freeze frame. A freeze frame consists of data values stored at a specific event; such as an engine malfunction of some kind.

Mode $03 – Request Emission-Related Powertrain Diagnostic Trouble Codes - The purpose of this service is to enable the external test equipment to obtain “confirmed” emission-related DTCs. Mode $04 – Clear/Reset Emission-Related Diagnostic Information - The purpose of this service is to provide a means for the external test equipment to command ECUs to clear all emission-related diagnostic information. This includes:

€ € € € € € € € € € € € €

Number of diagnostic trouble codes Diagnostic trouble codes Trouble codes for Freeze Frame data Freeze Frame data O2 test data Status of system monitor tests On-board monitor test results Travelled distance with activated MIL Number of warm startups since DTC clear Travelled distance since DTC clear Engine runtime (minutes) with MIL activated Time since DTC clear as well as learned adaptive values of the injection system.

Other manufacturer specific clear/reset actions might be possible.

Mode $05 – Request Oxygen Sensor Monitoring Test Results - The purpose of this service is to allow access to the on-board oxygen sensors monitoring test results.

Mode $06 – Request On-Board Monitoring Test Results for Non- Continuously Monitored Systems - This service gives access to the results for on-board diagnostic monitoring tests of specific components/systems that are not continuously monitored.

Examples of this are catalyst monitoring and the evaporative system monitoring.

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ScanMaster-ELM Mode $07 – Request On-Board Monitoring Test Results for Continuously Monitored Systems - Through this service, the external test equipment, can obtain test results for emission-related Powertrain components/systems that are continuously monitored during normal driving conditions.

Mode $08 – Request Control of On-Board System, Test or Component - This service enables external test equipment to control the operation of an on-board system, test or component.

Mode $09 – Request Vehicle Information - This service gives access to vehicle specific vehicle information such as Vehicle Identification Number (VIN) and Calibration IDs.

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Reading Performance Information Data (PID) Posted by Alex (Im) E. on 01 February 2013 12:11 AM PIDS are the serial data that can be accessed from the vehicle computer using a scan tool. PIDS include: 

Status of the OBD II System Component Monitors (Ready or Complete, or Not Ready or Incomplete)



Live Sensor Data (Oxygen sensor rich/lean indication, coolant temperature, MAP value, TPS value, vehicle speed, mass air flow, ambient temperature, engine rpm, etc.)



Status of Switches or Devices (cruise control on/off. brake pedal switch on/off. TCC engaged/disengaged, etc.)



Long and Short Term Fuel Trim, O2 sensor cross counts, injector duration.

DIAGNOSTIC VALUE PIDS provide valuable diagnostic information when checking the operation or status of various sensors, circuits and switches in the vehicle's engine management system.

For example, if the MIL lamp is on and you find an oxygen sensor code, you can call up the oxygen sensor PIDS on your scan tool display to see what the oxygen sensor is telling the PCM. You can also compare PIDS to see how one component may be affecting another.

For example, when you suddenly open the throttle on an idling engine, rpm should increase, the TPS reading should change and the MAP sensor value should drop.

PIDS can also be compared using a "graphing multimeter" or on a scope that converts the voltage values to waveforms.

Comparing the waveforms of several related sensors can help you find faults that might otherwise be impossible to detect.

SCAN TOOL PID CAPABILITY Different scan tools have different capabilities to display PIDS. The OEM scan tools used by new car dealers are capable of displaying every possible PID value that is built into the engine management system.

Most general purpose aftermarket scan tools do not contain the software that allows them to match the OEM scan tools in every respect -- but for most applications they can display all the important PIDS. The trouble is you never know what PIDS are missing until you go looking for one and find it isn't there.

Bummer.

That's why many professional technicians own multiple scan tools: an aftermarket general purpose scan tool, and one or more OEM scan tools for the makes they most frequently work on.

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Scan tools like TOAD support various PIDS including live data values, the status of switches and other devices, the readiness status of various OBD II monitors, and other test results.

Live data provides real-time measurements of system inputs.

Statuses tell you if a switch, relay or other device is ON/OFF or has been commanded ON or OFF. Readiness monitors tell you if the monitors have completed or not.

Test results are measured by the PCM and compared against preprogrammed pass/fail values in teh PCM's memory.

LIVE DATA: 

Air Flow Rate From MAF -- The airflow rate as measured by the mass air flow sensor.



Absolute Throttle Position -- The absolute throttle position (not the relative or learned) throttle position. Usually above 0% at idle and less than 100% at full throttle.



Calculated Load Value -- Indicates a percentage of peak available torque. Reaches 100% at wide open throttle at any altitude or RPM for both naturally aspirated and boosted engines.



Engine Coolant Temperature -- Engine coolant temperature as read by the engine coolant temperature sensor. This value should be compared to the actual coolant temperature to see if they match.

You can use an infrared thermometer or other thermometer to measure the temperature of the coolant at the thermostat outlet. If the actual temperature and displayed temperature do not match, it would tell you the coolant sensor is not reading correctly.



Engine RPM -- The current engine speed in revolutions per minute (RPM).



Fuel Rail Pressure -- Pressure in the fuel rail when the reading is referenced to atmosphere (gauge pressure).



Ignition Timing Advance -- Degrees of ignition timing (spark) advance for #1 cylinder (not including mechanical advance). Intake Manifold



Pressure -- Pressure in the intake manifold derived from a Manifold Absolute Pressure (MAP) sensor.



Long Term Fuel Trim (LTFT) -- The correction factor (percentage) being used by the fuel control system in both open and closed loop modes of operation. LTFT should typically be within plus or minus five. Positive LTFT numbers indicate the PCM is adding more fuel to compensate for a lean fuel condition.

Negative LTFT numbers mean the PCM is delivering less fuel to compensate for a rich fuel condition. If the LTFT is higher than 10 either way, it may indicate a problem.



Short Term Fuel Trim (STFT) -- The correction factor being used in closed loop by the PCM to maintain a balanced fuel mixture. If the fuel system is open loop, 0% correction should be reported. As with LTFT, the number should usually be plus or minus five. If greater than 10, it indicates a fuel mixture problem.



O2 Sensor Output Voltage -- The actual voltage being generated by the oxygen sensor (should be 0.1 to 1.0 volts for a conventional zirconia O2 sensor).

For wide-band O2 sensors and linear O2 sensors, the value may be higher, or it may be converted to a

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zero to one volt scale.

There may be multiple O2 sensor PIDS depending on homw many sensors the engien has (Bank1 sensor 1, Bank2 Sensor 1, etc.). 

Time Since Engine Start -- Shows the time the engine has been running since it was last started.

Vehicle Speed -- Displays vehicle road speed as read by the vehicle speed sensor (VSS).



Absolute Load Value -- This is the normalized value of air mass per intake stroke displayed as a percent.



Absolute Throttle Position -- The absolute throttle position (not the relative or learned) throttle position. Usually above 0% at idle and less than 100% at full throttle.



Accelerator Pedal Position -- The absolute pedal position (not the relative or learned) pedal position.

Usually above 0% at idle and less than 100% at full throttle.



Ambient Air Temperature -- The ambient air temperature as ready by the air temperature sensor. This value can be compared to the temperature reading by another thermometer to see if the values match.

If they do not, the air temperature sensor is not reading accurately.

NOTE: the temperature reading will depend on the location of the sensor. If the sensor is located under the hood, it may read higher than the outside temperatrue when the vehicle is not moving becuase of engine heat.



Barometric Pressure -- Barometric pressure as determined by a barometric pressure (BARO) sensor.

Note some weather services report barometric pressure adjusted to sea level. In these cases, the reported value may not match the displayed value.



Catalyst Temp -- The temperature inside the catalytic converter.



Commanded EGR -- Tells you what the PCM is commanding the EGR valve to do.

The percentage vlue should be 0% when EGR is commanded off (at idle), 100% when EGR is commanded on (typically when cruising under light load), and between 0% and 100% is the EGR solenoid is duty cycled on and off by the PCM (depending on vehicle speed, engine load and temperature).



Commanded Equivalence Ratio -- Fuel systems that use conventional oxygen sensor displays the commanded open loop equivalence ratio while the system is in open loop. Should report 100% when in closed loop fuel.

To obtain the actual air/fuel ratio being commanded, multiply the stoichiometric A/F ratio by the equivalence ratio. For example, gasoline, stoichiometric is 14.64:1 ratio.

If the fuel control system was command an equivalence ratio of 0.95, the commanded A/F ratio to the engine would be 14.64 * 0.95 = 13.9 A/F.



Commanded Evaporative Purge -- This value should read 0% when no purge is commanded and 100% at the maximum commanded purge position/flow.



Commanded Throttle Actuator -- This value should be 0% when the throttle is commanded closed and 100% when the throttle is commanded open.



Control Module Voltage -- Power input to the control module. Normally, this should show battery voltage minus any voltage drop between the battery and the control module (which should be less than a few tenths of a volt).

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Distance Since DTCs Cleared -- How many miles the vehicle has been driven since any DTCs were cleared with a scan tool. Distance 

Traveled While MIL On -- Tells you how many miles the vehicle has been driven with the MIL light on.

Also tells you how long the driver has been ignoring the light!



EGR Error -- Calculated error as percent of actual commanded EGR. Negative percent is less than commanded and positive is more than commanded. The greater the value, the more likely the EGR valve is sticking.



EVAP Purge -- This value is displayed as a percentage and is normalized for all types of EVAP systems. When EVAP purge is commanded off, the value should be o%, and 100% when it is commanded on.

This is an important value o check if the engine has lower than normal LTFT and STFT fuel trim numbers (indicating a rich fuel condition). The purge valve may be leaking vapor into the intake manifold.

To eliminate the purge valve as a possible source of fuel vapor, pinch off the purge vapor hose, run the engine and recheck the STFT number. If it is back to normal, the purse valve is leaking.



EVAP System Vapor Pressure -- Evaporative system vapor pressure normally obtained from a sensor located in the fuel tank.



Fuel Level Input -- Indicates the nominal fuel tank liquid fill capacity as a percent of maximum.



Fuel Rail Pressure -- Indicates the fuel rail pressure at the engine referenced to atmosphere (gauge pressure).



Fuel Rail Pressure Rel Manifold -- The fuel rail pressure referenced to the manifold vacuum (relative pressure).



Intake Air Temperature -- The temperature of the air in the intake manifold as read by the intake manifold air temperature sensor. This should be the same as ambient temperature in a cold engine that has not been started, and should be higher than ambient tempertarue if teh engine is warm and has been running.



Minutes Run with MIL On -- Accumulated minutes of engine run time while the MIL light is on.



O2 Sensor Wide Range mA -- Milliamp current for linear or wide-ratio oxygen sensors.



O2 Sensor Wide Range V -- Voltage for linear or wide-ratio oxygen sensors.



Relative Throttle Position -- Relative or learned throttle position.



Time Since DTCs Cleared -- Accumulated time since DTCs where cleared with a scan tool.



Warm-ups Since DTCs Cleared -- Number of warm-up cycles since all DTCs were cleared with a scan tool. A warm-up is defined as the coolant temperature rising by at least 22°C (40°F) and the engine temperature reaches at a minimum 70°C (160°F), or 60°C (140°F) for diesel engines.

TROUBLE CODES AND FREEZE FRAME DATA

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Code readers and scan tools will also display Stored Diagnostic Trouble Codes (DTCs), usually in numeric order.

Many scan tools can also display Pending Trouble Codes.

These are codes that indicate a fault has been detected, but that the fault has not yet repeated.

If the fault repeats under similar driving conditions, it will usually cause the Pending Code to become a Stored Code and turn on the MIL light.

Many scan tools can also display Freeze Frame data.

These are PIDS that are captured when a fault occurs so you can refer to them later when diagnosing the problem.

Freeze frame data typically includes related sensor values at the time the fault occurred.

STATUS AND READINESS MONITORS OBD II requires the following status and readiness monitors: 

Fuel System 1 Status



Fuel System 2 Status



Secondary Air Status



Auxiliary Input Status



Misfire Monitor Status



Fuel System Status



Comprehensive Component Monitoring Status



Catalyst Monitoring Status



Heated Catalyst Monitoring Status



Evaporative System Monitoring Status



Secondary Air System Monitoring Status



A/C System Refrigerant Monitoring Status



Oxygen Sensor Monitoring Status



Oxygen Sensor Heater Monitoring Status



EGR System Monitoring Status



ECU Oxygen Sensor Test Results

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Shopping Tips for Selecting an OBDII compatible scantool There are a growing number of scantools compatible with 1996 and newer vehicles with a wide variety of features. With prices ranging from $250 to $2500 anyone looking for a scantool needs to do a little homework to find a tool that best fits their needs.

Will it work on your vehicle?

First and foremost, the tool you purchase must support the vehicles you anticipate working on.

Although it's true that OBDII is a standard, there are five different types of hardware communications used by OBDII vehicles. Some tools support all five and some are manufacturer specific.

Supported parameters Not all scantools are equal. In fact, some aren't even close. As part of the OBDII standard, the US Environmental Protection Agency mandated that a basic set of emissions related readings be supported on all OBDII vehicles. The SAE specification J1979 defines these legislated parameters. Many low-end tools only support these emissions related readings, giving you access to only a dozen or so truly useful parameters. While these give you some basic vehicle information, they are just a small set of the vehicle information available through the OBDII port.

Is it upgradeable?

Each year vehicle manufacturers release new models and revise existing models. For a scantool to fully support the new vehicles, it must typically be updated. Professional quality scantools are updateable, although often at a price of $500 or more per update. Most lower end handheld scantools are not updateable. Check what updates will cost before committing to a tool.

Built in help For anyone working on his or her own vehicle, the Factory Service Manual is a must-have. But the scantool itself may be able to provide some of that necessary information. When a DTC is set, does the tool display the DTC number or give the full definition? A tool that displays the full definition will save a lot of time and frustration. Does the tool offer any information on typical readings to explain what the reading is? A simple sentence or two of explanation can save a lot of trips back and forth to the shop manual.

Data logging or storage A sure way to park your car in a ditch is to try and watch a scantool display while doing a roadtest. A tool that stores data to allow safe viewing back at the garage is a must. Be certain that the tool you buy has this capability.

[ OBD-II Home ]

The OBD-II Home Page is hosted by © 2011 B&B Electronics

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How Car Diagnostic Software and Tools Work February 17, 2012 Most car diagnostic software is based on reading data from your vehicle's OBD-II (onboard diagnostic) system. Learn how to use a car diagnostic tool.

Car diagnostic software helps keep your vehicle running smoothly. This software is built into all cars made after 1996, and it is included in many earlier cars as well. The latest technology is called OBDII, which stands for on board diagnostic system. The OBD-II is incredibly useful to mechanics and other people curious about the status of their vehicle when something seems to go wrong.

Positioning of the Software The OBD-II system in your vehicle has sensors and ports in various parts of the car. There is one underneath the dash of most cars, and many vehicles also have a port under to the driver's seat.

There are other sensors and activation centers spread throughout the vehicle in order to monitor the activity of various parts of the car. Essentially, the software is located all throughout the vehicle.

Function of the Software The OBD-II monitors the proper functioning of your vehicle. It not only controls certain engine functions through the on board computer, it also keeps a record of all of the things that happen to your car as you drive it, good and bad. This information can be used later by mechanics, who download a series of diagnostic codes from the OBD-II port. These codes explain what is going on with the vehicle, and are the basis for the diagnosis of your problem and how to fix it when the check engine light comes on or if you experience other problems.

Process The software that measures the diagnostics of your car takes regular readings of different systems in the car. This is primarily centered on the engine, but the OBD-II includes sensors for the chassis, frame and other parts of the car too. At each reading, the software records a particular acronym or code that represents the functionality of that system. This information is stored within the OBD-II system and can be retrieved by attaching a computer to the port. The mechanic then downloads the codes and translates them to determine exactly what was going on at each point of inspection. This helps to calculate when and how damage occurred to a part of your car.

How to Use a Car Diagnostic Tool An auto scan tool can be used to read the diagnostic software. Also called a car code reader or an OBD-II scanner, this tool is a useful way to determine the issues with your car without having to take it in to a dealership or a mechanic for an expensive analysis.

You'll need the following materials in order to take a diagnostic reading of your car:

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

A Laptop, iPhone or iPod Touch



Jack cables and a port connector



A scanner or car code reader



A breakdown of codes and acronyms for your vehicle

Install the Computer Software Computer scanner systems require that you connect the scanner to a computer. An iPhone or iPod Touch will also work with devices such as the REV iPhone Car Diagnostic Tool. In order to get a reading from the car diagnostic device, install the software that comes with the scanner system. This allows the computer to display the readings from the diagnostic tool.

Connect the Scanner Find the port where you can attach the scanner. This port is often located on the dash, typically just below the steering wheel and to one side or another. Look for a small indentation and a simple port system. The port connector may also be underneath the driver's side of the front seat. If you're having a hard time figuring out where to connect your scanner, check the owner's manual for your car or consult with a professional.

Get a Reading Follow the instructions from the scanner tool and the software on your computer to take a reading of the car diagnostic device. This will help you to determine exactly what the problem is by sending a series of codes to your computer, which will be displayed.

Translate the Codes Using the guidelines from the code translation sheet, figure out the problem that has caused the malfunction or the check engine light to come on. You can then decide the best way to remedy the problem or take your car to a mechanic.

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CHOOSING THE RIGHT SCAN TOOL THE FOUR CRITICAL STEPS TO CHOOSING A SCAN TOOL THAT’S RIGHT FOR YOUR SHOP BRYCE EVANS

STAFF GRAPHIC THE FOUNDATION OF A PROPER REPAIR IS “IN THE PREPARATION,” SAYS ROBBIE BERMAN. AN HOUR OF PREP TIME BEFORE A JOB CAN CUT OUT SUPPLEMENTS, ELIMINATE DELAYS IN PARTS ORDERING, SHAVE CYCLE TIME AND, ULTIMATELY, IMPROVE THE FINAL PRODUCT AND THE CUSTOMER EXPERIENCE. THIS SHOULD BE OBVIOUS TO EVERY SHOP, BERMAN SAYS, BUT TOO OFTEN IT’S NOT. BERMAN STARTED HIS CAREER AND HIS SHOP, ROBBIE’S AUTOMOTIVE AND COLLISION SPECIALISTS IN WHARTON, N.J., WITH A FOCUS ON MECHANICAL REPAIR. AND HE SAYS THAT IF THERE’S ONE THING THE COLLISION INDUSTRY CAN LEARN FROM MECHANICAL SHOPS, IT’S THE IMPORTANCE OF DIAGNOSTICS. “DIAGNOSTICS IS EVERYTHING, AND IT’S ONLY GROWING.” HE SAYS. “EVERY CAR COMING DOWN THE ROAD HAS MORE AND MORE TECHNOLOGY IN IT, MORE AND MORE COMPUTER SYSTEMS. WITHOUT THE RIGHT DIAGNOSTIC EQUIPMENT AND PROCESSES, YOU’RE NOT GOING TO BE ABLE TO FIX VEHICLES ANYMORE.” DIAGNOSTIC SCAN TOOLS ARE SOMETHING THAT HIS $4 MILLION, 10,000-SQUARE-FOOT COLLISION BUSINESS HAS INVESTED IN FOR YEARS, BUT AS AN INDUSTRY, BERMAN SAYS, IT’S SOMETHING THAT TOO MANY SHOPS ARE MISSING OUT ON. BOB KEITH, SHOP OWNER AND DIRECTOR OF EDUCATION AND TRAINING WITH CARSTAR, AGREES.

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AND, LIKE ANY EQUIPMENT OR TOOL PURCHASE A SHOP CAN MAKE, INVESTING IN DIAGNOSTIC SCAN TOOLS IS EXACTLY THAT—AN INVESTMENT, SOMETHING SHOPS NEED TO RESEARCH, UNDERSTAND AND WEIGH OPTIONS ON BEFORE PURCHASING. WHEN IT COMES TO SCAN TOOLS, THERE ARE DOZENS AND DOZENS OF OPTIONS FOR COLLISION FACILITIES. BERMAN AND KEITH HELPED FENDERBENDER SIMPLIFY THE PURCHASING PROCESS, OFFERING THEIR TIPS ON MATCHING YOUR BUSINESS TO THE RIGHT TOOL. UNDERSTAND THE VALUE KEITH LIKES TO KEEP THINGS LIGHTHEARTED IN HIS NATIONWIDE TRAINING COURSES HE RUNS FOR CARSTAR, AND, IN DEALING WITH THE TOPIC OF TOOL AND EQUIPMENT PURCHASES, HE LIKES TO POINT TO A ONE-PANEL COMIC. THERE ARE A NUMBER OF VERSIONS, BUT THE GENERAL PICTURE IS THIS: A GROUP OF KNIGHTS ARE GRABBING THEIR SWORDS AND STRAPPING ON ARMOR, GETTING READY FOR BATTLE. BEHIND THEM STANDS A SALESMAN WITH A MACHINE GUN LOADED INTO A WAGON. THE CAPTION, COMING FROM THE LEADER OF THE KNIGHTS, SAYS, “CAN’T THEY SEE WE DON’T HAVE TIME FOR THIS? WE HAVE A BATTLE TO FIGHT!” “IT CRACKS ME UP, BECAUSE YOU TALK TO A LOT OF SHOPS AROUND THE COUNTRY, AND THAT’S THE APPROACH THEY TAKE TO TOOLS AND EQUIPMENT,” HE SAYS. “PEOPLE LOOK AT IT AS A COST. TO AN EXTENT, IT IS, BUT YOU HAVE TO UNDERSTAND THE INVESTMENT AND THE BENEFITS IT CAN BRING. IT’S EASY TO GET TOO CAUGHT UP IN WHAT YOU’RE DOING TO TAKE A MOMENT AND LOOK AT THE BIGGER PICTURE OF HOW THAT INVESTMENT WILL AFFECT YOUR BUSINESS.” EVEN BASIC, AFTERMARKET SCAN TOOLS COME WITH A FIVE-FIGURE PRICE TAG, BERMAN SAYS, RANGING FROM $10,000–$30,000. THEN, THERE’S ANNUAL SUBSCRIPTION FEES (NORMALLY AROUND $1,500) TO THE VEHICLE INFORMATION THE DEVICES READ. IT’S A SUBSTANTIAL INVESTMENT FOR A COLLISION SHOP TO MAKE, BUT WITHOUT IT, WELL, YOU’RE SIMPLY OPTING TO USE A SWORD OVER A MACHINE GUN. “THE BENEFITS OF HAVING THE RIGHT TOOL, THE ONE THAT FITS INTO YOUR BUSINESS, FAR OUTWIEGHS THE COST,” BERMAN SAYS. “YOU’RE INVESTING IN YOUR SHOP’S ABILITY TO PROPERLY PERFORM WORK NOW AND IN THE FUTURE.” THERE ARE FIVE CRITICAL STEPS TO ENSURE YOUR SHOP CHOOSES THE CORRECT SCAN TOOL. STEP 1: IDENTIFY YOUR NEED. WITH THE INCREASE OF IN-VEHICLE TECHNOLOGY AND COMPUTER SYSTEMS, BERMAN SAYS EVERY SHOP NEEDS PROPER DIAGNOSTIC EQUIPMENT REGARDLESS OF THEIR WORK MIX. HOWEVER, WHICH TOOL (OR TOOLS) YOU CHOOSE IS 100 PERCENT DETERMINED BY THAT WORK MIX. BOTTOM LINE: YOU NEED TO INVEST IN THE TOOLS TO FIX THE VEHICLES YOU WORK ON THE MOST. BERMAN SUGGESTS TAKING A HARD LOOK AT THE VEHICLES YOUR SHOP REPAIRS, RANKING THEM FROM MOST FREQUENT TO LEAST FREQUENT. THE TOP-10 VEHICLES, HE SAYS, ARE THE ONES YOU NEED TO FOCUS YOUR EFFORTS ON. “IT WOULD BE GREAT TO GO TO 20 MAKES AND MODELS, OR 30, BUT IT’S UNLIKELY YOU’RE GOING TO HAVE THE FUNDING FOR THAT,” HE SAYS. “IF YOU FOCUS ON THE ONES YOU NEED THE MOST—AND THAT’D BE THAT TOP 10—YOU’RE GOING TO BE ABLE TO PROPERLY DIAGNOSE THE VAST MAJORITY OF VEHICLES THAT ENTER YOUR SHOP.”

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REMEMBER, BERMAN SAYS, THAT MANY SCAN DEVICES WORK FOR MULTIPLE MAKES, MODELS AND YEARS—MEANING THAT THE TOOL(S) YOU CHOOSE TO SUPPORT THOSE 10 VEHICLE MAKES VERY LIKELY COULD COVER NEARLY EVERY VEHICLE YOU WORK ON. WHICH BRINGS US TO …

STEP 2: RESEARCH TOOLS. THIS IS WHERE THE PROCESS MAY SEEM DAUNTING, BERMAN SAYS, BUT IT DOESN’T NEED TO. IF YOU HAVE AN UNDERSTANDING OF WHAT YOU NEED THE TOOL(S) TO DO (E.G., PROPERLY DIAGNOSE THOSE 10 VEHICLE LINES), THEN THE SITUATION IS ALREADY SIMPLIFIED. WHEN LOOKING AT SCAN TOOLS, BERMAN SUGGESTS FOCUSING ON THESE FIVE CHARACTERISTICS OF THE TOOL AND THE COMPANY THAT PROVIDES IT: 1. COVERAGE. DEPENDING ON THE BRAND, WHETHER IT’S AN OEM OR AFTERMARKET TOOL, AND THE VARIOUS MODELS, EACH SCAN TOOL IS GOING TO BE ABLE TO PROVIDE DIFFERENT INFORMATION TO A REPAIRER. THEY WILL HAVE DIFFERENT ACCESS TO MANUFACTURER CODES, AND THEY WILL BE ABLE TO ACCESS DIFFERENT LEVELS OF THE VEHICLE’S SYSTEMS. AS BERMAN POINTS OUT, YOUR TOOL NEEDS TO COVER ALL ASPECTS OF EVERY ONE OF YOUR TOP-10 VEHICLES. 2. TRAINING/EASE OF USE. BERMAN SAYS THERE CAN BE A DRASTICALLY DIFFERENT LEARNING CURVE BETWEEN BRANDS AND MODELS OF SCAN TOOLS. IN HIS SHOP, HE HAS TWO DIFFERENT AFTERMARKET SCAN TOOLS—ONE FROM SNAP-ON AND ANOTHER FROM OTC—AND EACH, HE SAYS, ARE RELATIVELY SIMPLE TO USE, AND BOTH COMPANIES PROVIDE AMPLE TRAINING. 3. TECHNICAL SUPPORT. THERE ARE STILL GOING TO BE TIMES WHEN A TECHNICIAN IS UNABLE TO PULL A CODE, OR A CODE MAY NOT MAKE SENSE TO THE ISSUES THE VEHICLE HAS. BERMAN SAYS THIS IS WHY HAVING STRONG TECHNICAL SUPPORT FROM THE COMPANY THAT PROVIDES THE TOOL CAN HELP YOU UNDERSTAND WHETHER THERE IS AN ISSUE WITH THE TOOL ITSELF OR SIMPLY USER ERROR. 4. UPGRADES AND UPDATES. THE MAKEUP OF VEHICLES CHANGES RAPIDLY, AND BERMAN SAYS TO MAKE SURE YOU HAVE A TOOL THAT KEEPS UP WITH THE LATEST NEEDS OF REPAIRERS— EITHER THROUGH SUBSCRIPTION UPDATES OR UPGRADES TO THE TOOL ITSELF. SOME COMPANIES PROVIDE TRADE-IN OFFERS FOR UPGRADES, HE SAYS. 5. COST. THIS IS OBVIOUSLY AN IMPORTANT ASPECT, BUT BOTH KEITH AND BERMAN SAY TO KEEP IT LAST ON THIS LIST. COST IS ONLY RELATIVE TO THE EFFECT THE TOOL WILL HAVE ON YOUR BUSINESS, WHICH CAN EASILY BE MEASURED IN THE NEXT STEP. STEP 3: ANALYZE THE RETURN ON INVESTMENT (ROI).

KEITH SAYS THAT, DESPITE WHAT SOME PEOPLE ASSUME ABOUT ROI, IT CAN ACTUALLY BE PROPERLY CALCULATED BEFORE A PURCHASE IS EVER MADE. HERE ARE HIS THREE SIMPLE STEPS TO DOING THAT: 1. STUDY THE PROBLEM. IN THE CASE OF A SCAN TOOL PURCHASE, KEITH SAYS TO LOOK AT HOW THE CURRENT PROCESS PLAYS OUT IN YOUR SHOP WITHOUT THE NEW TOOL. LOOK FOR THE INEFFICIENCIES: ARE YOUR TECHS FORCED TO SHARE OR SEARCH FOR THE CURRENT TOOLS? DO THEY HAVE TO OUTSOURCE THE WORK BECAUSE YOU DON’T HAVE ONE AT ALL? WHAT’S THE LOSS IN PRODUCTIVITY, CYCLE TIME, SALES, REVENUE AND PROFIT? ADD IT UP, KEITH SAYS, AND SEE HOW MUCH YOUR SHOP IS LOSING IN BOTH EFFICIENCY OR DOLLARS. PUT A NUMBER TO IT. 2. UNDERSTAND HOW THE NEW TOOL MAKES A DIFFERENCE. BECAUSE YOU HAVE AN IDEA OF THE TOOLS YOU’D LIKE TO PURCHASE FROM STEP 2, YOU CAN ANALYZE HOW THE NEW TOOL WILL AFFECT THOSE EFFICIENCY AND REVENUE NUMBERS. HOW MUCH TIME DOES IT SHAVE OFF

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IN PRODUCTION? HOW MUCH MONEY DOES IT ADD TO YOUR SHOP’S SALES? AGAIN, PUT A NUMBER TO IT. 3. COMPARE SAVINGS TO COST. KEITH SAYS THE FINAL STEP IS TO SIMPLY COMPARE THE POTENTIAL MONEY SAVED AND THE IMPROVED EFFICIENCY CREATED TO THE TOTAL COST OF THE TOOL INCLUDING SUBSCRIPTIONS. THAT’S YOUR ESTIMATED ROI, AND IT SHOULD GIVE YOU A GOOD SENSE OF HOW LONG IT WILL TAKE TO ACHIEVE THAT BREAK-EVEN POINT. NOTE THAT THIS CALCULATION IS TO HELP YOU BEST DETERMINE THE QUALITY OF YOUR PURCHASE; EVERYDAY BUSINESS SITUATIONS CAN CAUSE CHANGES DOWN THE ROAD. STEP 4: IMPLEMENT THE TOOL WORKING THROUGH THE FIRST THREE STEPS SHOULD PROVIDE YOU WITH A TOOL OR LIST OF TOOLS THAT WILL IMPROVE YOUR BUSINESS’S EFFICIENCY AND SALES—AT LEAST, IN THEORY. THE KEY TO MAKING THAT PURCHASE, OR PURCHASES, TRULY HAVE VALUE IN YOUR SHOP COMES FROM PROPER IMPLEMENTATION, KEITH SAYS. BERMAN SAYS TO CREATE A STANDARD OPERATING PROCEDURE IN YOUR SHOP THAT OUTLINES WHEN THE TOOL SHOULD BE USED AND WHO IS ASSIGNED TO PERFORM THE SCAN. IN BERMAN’S SHOP, HE HAS TWO OF HIS TECHNICIANS FROM THE MECHANICAL SEGMENT PERFORM THE SCANS BOTH DURING THE BLUEPRINTING PROCESS AND AFTER THE REPAIR IS COMPLETED.

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ProScan Help : Diagnostic Trouble Code Breakdown

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ProScan Help : Diagnostic Trouble Code Breakdown DTCs are composed of five characters; one letter followed by 4 digits.

Example DTCs: 

P0134



P1155



B0042



C1132



U3201

Digit 1 = System Identifier Digit 1

System

P

Powertrain

B

Body

C

Chassis

U

Undefined

Digit 2 = Type of Code Definition Generic: Same definition for all manufacturers.

Manufacturer-Specific: Definition varies among manufacturers.

Digit 2

Type of Code Definition

0

Generic

1

Manufacturer-Specific

2

P2xxx = Generic B2xxx = Manufacturer-Specific C2xxx = Manufacturer-Specific U2xxx = Manufacturer-Specific

3

P30xx – P33xx = Manufacturer-Specific

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ProScan Help : Diagnostic Trouble Code Breakdown

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P34xx – P39xx = Generic B3xxx = Generic C3xxx = Generic U3xxx = Generic Digit 3 = Sub-System Digit 3

Sub-System

1

Fuel & Air Metering

2

Fuel & Air Metering (Injector Circuit Malfunction Only)

3

Ignition System or Misfire

4

Auxiliary Emission Control System

5

Vehicle Speed Control & Idle Control System

6

Computer Output Circuits

7-8

Transmission

Digits 4 & 5 The fourth and fifth digits of the DTC identify the specific problem.

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ProScan Help : Oxygen Sensor and Catalyst Configurations

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ProScan Help : Oxygen Sensor and Catalyst Configuration Example

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ProScan Help : Oxygen Sensor and Catalyst Configurations

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OBDII: PAST, PRESENT & FUTURE

All 1996 and newer model year passenger cars and light trucks are OBDII-equipped, but the first applications were actually introduced back in ‘94 on a limited number of vehicle models.

What makes OBDII different from all the self-diagnostic systems that proceeded it is that OBDII is strictly emissions oriented. In other words, it will illuminate the Malfunction Indicator Lamp (MIL) anytime a vehicle’s emissions exceed 1.5 times the federal test procedure (FTP) standards for that model year of vehicle. That includes anytime random misfires cause an overall rise in HC emissions, anytime the operating efficiency of the catalytic converter drops below a certain threshold, anytime the system detects air leakage in the sealed fuel system, anytime a fault in the EGR system causes NOX emissions to go up, or anytime a key sensor or other emission control device fails. In other words, the MIL light may come on even though the vehicle seems to be running normally and there are no real driveability problems.

The main purpose of the MIL lamp on an OBDII-equipped vehicle, therefore, is to alert you when your vehicle is polluting so you’ll get their emission problems fixed. But as we all know, its easy to ignore warning lamps— until steam is belching from under the hood or the engine is making horrible noises. That’s why regulators want to incorporate OBDII into existing and enhanced vehicle emissions inspection programs. If the MIL lamp is found to be on when a vehicle is tested, it doesn’t pass even if its tailpipe emissions are within acceptable limits.

WHY OBDII? The problem with most vehicle inspection programs is that they were developed back in the 1980s to identify "gross polluters." The tests were designed primarily to measure idle emissions on carbureted engines (which are dirtiest at idle), and to check for only two pollutants: unburned hydrocarbons (HC) and carbon monoxide (CO).

The pass/fail cut points that were established for the various model years were also made rather lenient to minimize the number of failures. Consequently, a lot of late model vehicles that shouldn’t be passing an emissions test are getting through anyway.

Efforts to upgrade vehicle inspection programs to the new I/M 240 standards have stalled because of a lack of public and political support. The I/M 240 program would have required "loaded-mode" emissions testing on a dyno while the vehicle was driven at various speeds following a carefully prescribed driving trace. While this was going on, the tailpipe gases would be analyzed to check not only for total emissions. The total emissions for the entire 240-second driving cycle would then be averaged for a composite emission score that determines whether or not the vehicle passed the test. Also included would be an evaporative purge flow test to measure the flow rate of the canister purge valve, and an engine off pressure test of the evaporative emission control system to check the fuel tank, lines and cap for leaks.

The I/M 240 program was to have been required in most areas of the country that don’t meet national ambient air quality (NAAQ) standards. But after the program faltered in Maine, most states balked and only Colorado went ahead with the program. The cost and complexity of the I/M 240 program combined with less than enthusiastic public acceptance doomed it from the start. So it’s now up to the individual states to come up with alternative plans for improving their air quality. An important element in many of those plans is OBDII. A SHORT HISTORY WITH FAR REACHING IMPLICATIONS The origins of OBDII actually date back to 1982 in California, when the California Air Resources Board (ARB) began developing regulations that would require all vehicles sold in that state starting in 1988 to have an onboard diagnostic system to detect emission failures. The original onboard diagnostic system (which has since become known as OBDI) was relatively simple and only monitored the oxygen sensor, EGR system, fuel delivery system and engine control module.

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OBDI was a step in the right direction, but lacked any requirement for standardization between different makes and models of vehicles. You still had to have different adapters to work on different vehicles, and some systems could only be accessed with costly "dealer" scan tools. So when ARB set about to develop standards for the current OBDII system, standardization was a priority: a standardized 16-pin data link connector (DLC) with specific pins assigned specific functions, standardized electronic protocols, standardized diagnostic trouble codes (DTCs), and standardized terminology.

Another limitation of OBDI was that it couldn’t detect certain kinds of problems such as a dead catalytic converter or one that had been removed. Nor could it detect ignition misfires or evaporative emission problems.

Furthermore, OBDI systems would only illuminate the MIL light after a failure had occurred. It had no way of monitoring progressive deterioration of emissions-related components. So it became apparent that a more sophisticated system would be required. The California Air Resources Board eventually developed standards for the next generation OBD system, which were proposed in 1989 and became known as OBDII. The new standards required a phase-in starting in 1994. The auto makers were given until the 1996 model year to complete the phase-in for their California vehicles.

Similar standards were incorporated into the federal Clean Air Act in 1990 which also required all 49-state vehicles to be OBDII equipped by 1996 -- with one loophole. The OBDII systems would not have to be fully compliant until 1999. So some 1996 OBDII systems may lack one of the features normally required to meet the OBDII specs, such as the evaporative emissions purge test.

EARLY OBDII APPLICATIONS 1994 vehicles equipped with the early OBD II systems include Buick Regal 3800 V6, Corvette, Lexus ES3000, Toyota Camry (1MZ-FE 3.0L V6) and T100 pickup (3RZ-FE 2.7L four), Ford Thunderbird & Cougar 4.6L V8, and Mustang 3.8L V6.1995 vehicles with OBDII include Chevy/GMC S, T-Series pickups, Blazer and Jimmy 4.3L V6, Ford Contour & Mercury Mystique 2.0L four & 2.6L V6, Chrysler Neon, Cirrus and Dodge Stratus, Eagle Talon 2.0L DOHC (nonturbo), and Nissan Maxima and 240 SX. Not all of these early applications are fully OBDII compliant, but do include the major diagnostic features of the current system.

OBDII HARDWARE UPGRADES Don’t think for a moment that OBDII is just a fancier version of self-diagnostic software. It’s that and much, much more.OBDII-equipped vehicles typically have: •

Twice the number of oxygen sensors as non-OBDII vehicles(most of which are heated O2 sensors). The additional O2 sensors are located downstream of the catalytic converter.

•

More powerful powertrain control modules, with either16-bit (Chrysler) or 32-bit (Ford & GM) processors to handle up to 15,000 new calibration constants that were added by OBDII.

•

Electronically Erasable Programmable Read Only Memory(EEPROM) chips that allows the PCM to be reprogrammed with revised or updated software changes using a terminal link or external computer.

•

A modified evaporative emission control systems with a diagnostic switch for purge testing, or an enhanced EVAP system with a vent solenoid, fuel tank pressure sensor and diagnostic test fitting,

•

More EGR systems with a linear EGR valve that is electronically operated and has a pintle position sensor.

•

Sequential fuel injection rather than multiport or throttle body injection. Both a MAP sensor and MAF sensor for monitoring engine load and airflow.

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TOOLING UP FOR OBDII To work on your OBDII-equipped vehicle, you’ll need an OBDII scan tool such as AutoTap for PC or Palm PDA. THAT PESKY MIL LAMP Most technicians are pretty familiar with the operation of the "Check Engine" or "Malfunction Indicator Lamp" (MIL) on late model vehicles. But on OBDII-equipped vehicles, it may seem like the MIL lamp has a mind of its own.

On ‘96 General Motors J-, N- and H-body cars, several rental fleets have encountered problems with the MIL lamp coming on because motorists and fleet personnel haven’t been using the correct refueling procedure when filling the fuel tank with gas. On these cars, the OBDII system applies vacuum to the evaporative emissions control system to check for air leakage. If the gas cap isn’t tight or the tank is filled while the key is on or the engine is idling, it can trigger a false P0440 code causing the MIL light to come on. GM has not issued a technical service bulletin on the problem, but is advising its dealers and fleet customers to reflash the EEPROM with revised OBDII programming that waits to check the evaporative emissions system until the vehicle is in motion.

Bad gas has also been causing some false MIL lights. When the vehicle is diagnosed, the technician finds a P0300 random misfire code which would normally be set by a lean misfire condition due to a vacuum leak, low fuel pressure, dirty injectors, etc., or an ignition problem such as fouled plugs, bad plug wires, weak coil, etc.

The OBDII self-diagnostics tracks misfires by individual cylinder, and considers up to a 2% misfire rate as normal. But water in the gas or variations in the additive package in reformulated gasoline in some areas of the country can increase the misfire rate to the point where it triggers a code.

To minimize the occurrence of false MIL lamps, the OBDII system is programmed so that the MIL lamp only comes on if a certain kind of fault has been detected twice under the same driving conditions. With other faults (those that typically cause an immediate and significant jump in emissions), the MIL light comes on after only a single occurrence. So to correctly diagnose a problem, it’s important to know what type of code you’re dealing with.

Type A diagnostic trouble codes are the most serious and will trigger the MIL lamp with only one occurrence.

When a Type A code is set, the OBDII system also stores a history code, failure record and freeze frame data to help you diagnose the problem.

Type B codes are less serious emission problems and must occur at least once on two consecutive trips before the MIL lamp will come on. If a fault occurs on one trip but doesn’t happen again on the next trip, the code won’t "mature" and the light will remain off. When the conditions are met to turn on the MIL lamp, a history code, failure record and freeze frame data are stored the same as with Type A codes.

A drive cycle or trip, by the way, is not just an ignition cycle, but a warm-up cycle. It is defined as starting the engine and driving the vehicle long enough to raise the coolant temperature at least 40 degrees F (if the startup temperature is less than 160 degrees F).

Once a Type A or B code has been set, the MIL will come on and remain on until the component that failed passes a self-test on three consecutive trips. And if the fault involved something like a P0300 random misfire or a fuel balance problem, the light won’t go out until the system passes a self-test under similar operating conditions (within 375 rpm and 10% of load) that originally caused it to fail. That’s why the MIL lamp won’t go out until the emissions problem has been repaired. Clearing the codes with your AutoTap scan tool or disconnecting the powertrain control module’s power supply won’t prevent the lamp from coming back on if the problem hasn’t been fixed. It may take one or more driving cycles to reset the code, but sooner or later the MIL lamp will go back on if the problem is still there.

Likewise, the MIL won’t necessarily go on if you intentionally disconnect a sensor. It depends on the priority ranking of the sensor (how it affects emissions), and how many driving cycles it takes for the OBDII diagnostics to pick up the fault and set a code.

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As for Type C and D codes, these are non-emissions related. Type C codes can cause the MIL lamp to come on (or illuminate another warning lamp), but Type D codes do not cause the MIL lamp to come on.

RUNNING AN OBDII DRIVE CYCLE Suppose you’ve "fixed" an emissions problem on your OBDII-equipped vehicle. How can you check your work?

By performing what’s called an "OBDII drive cycle." The purpose of the OBDII drive cycle is to run all of the onboard diagnostics. The drive cycle shold be performed after you’ve erased any trouble codes from the PCM’s memory, or after the battery has been disconnected. Running through the drive cycle sets all the system status "flags" so that subsequent faults can be detected.

The OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F and the coolant and air temperature sensors within 11 degrees of one another).

NOTE: The ignition key must not be on prior to the cold start otherwise the heated oxygen sensor diagnostic may not run.

1. As soon as the engine starts, idle the engine in drive for two and a half minutes with the A/C and rear defrost on. OBDII checks oxygen sensor heater circuits, air pump and EVAP purge.

2. Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle. OBDII checks for ignition misfire, fuel trim and canister purge.

3. Hold at a steady state speed of 55 mph for three minutes. OBDII monitors EGR, air pump, O2 sensors and canister purge.

4. Decelerate (coast down) to 20 mph without braking or depressing the clutch. OBDII checks EGR and purge functions.

5. Accelerate back to 55 to 60 mph at ¾ throttle. OBDII checks misfire, fuel trim and purge again.

6. Hold at a steady speed of 55 to 60 mph for five minutes. OBDII monitors catalytic converter efficiency, misfire, EGR, fuel trim, oxygen sensors and purge functions.

7. Decelerate (coast down) to a stop without braking. OBDII makes a final check of EGR and canister purge.

BEYOND OBDII OBDII is a very sophisticated and capable system for detecting emissions problems. But when it comes to getting motorists to fix emission problems, it’s no more effective than OBDI. Unless there’s some means of enforcement, such as checking the MIL light during a mandatory inspection, OBDII is just another idiot light.

Currently under consideration are plans for OBDIII, which would take OBDII a step further by adding telemetry.

Using miniature radio transponder technology similar to that which is already being used for automatic electronic toll collection systems, an OBDIII-equipped vehicle would be able to report emissions problems directly to a regulatory agency. The transponder would communicate the vehicle VIN number and any diagnostic codes that were present. The system could be set up to automatically report an emissions problem via a cellular or satellite link the instant the MIL light comes on, or to answer a query from a cellular, satellite or roadside signal as to its current emissions performance status.

What makes this approach so attractive to regulators is its effectiveness and cost savings. Under the current system, the entire vehicle fleet in an area or state has to be inspected once every year or two to identify the 30% or so vehicles that have emissions problems. With remote monitoring via the onboard telemetry on an OBDIIIequipped vehicle, the need for periodic inspections could be eliminated because only those vehicles that reported problems would have to be tested.

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On one hand, OBDIII with its telemetry reporting of emission problems would save consumers the inconvenience and cost of having to subject their vehicle to an annual or biennial emissions test. As long as their vehicle reported no emission problems, there’d be no need to test it. On the other hand, should an emissions problem be detected, it would be much harder to avoid having it fixed—which is the goal of all clean air programs anyway. By zeroing in on the vehicles that are actually causing the most pollution, significant gains could be made in improving our nation’s air quality. But as it is now, polluters may escape detection and repair for up to two years in areas that have biennial inspections. And in areas that have no inspection programs, there’s no way to identify such vehicles. OBDIII would change all that.

The specter of having Big Brother in every engine compartment and driving a vehicle that rats on itself anytime it pollutes is not one that would appeal to many motorists. So the merits of OBDIII would have to be sold to the public based on its cost savings, convenience and ability to make a real difference in air quality. Even so, any serious attempt to require OBDIII in the year 2000 or beyond will run afoul of Fourth Amendment issues over rights of privacy and protection from government search and seizure. Does the government have the right to snoop under your hood anytime it chooses to do so, or to monitor the whereabouts of your vehicle? These issues will have to be debated and resolved before OBDIII stands a chance of being accepted. Given the current political climate, such drastic changes seem unlikely.

Another change that might come with OBDIII would be even closer scrutiny of vehicle emissions. The misfire detection algorithms currently required by OBDII only watch for misfires during driving conditions that occur during the federal driving cycle, which covers idle to 55 mph and moderate acceleration. It does not monitor misfires during wide open throttle acceleration. Full range misfire detection will be required for 1997 models.

OBDIII could go even further by requiring "fly-by-wire" throttle controls to reduce the possibility of misfires on the coming generation of low emission and ultra low emission vehicles.So until OBDIII winds its way through the regulatory process, all we have to worry about is diagnosing and repairing OBDII-equipped vehicles and all the non-OBD vehicles that came before them.

AutoTap – OBDII Automotive Diagnostic Tool http://www.autotap.com

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CHOOSING THE RIGHT SCAN TOOL FOR YOUR SHOP HOW CHOOSING THE RIGHT DIAGNOSTIC SCAN TOOL CAN INCREASE YOUR SHOP’S PROFITABILITY BRYCE EVANS

FIND THE RIGHT FIX EVERY SHOP HAS DIFFERENT USES FOR DIAGNOSTIC EQUIPMENT, MAKING IT CRITICAL TO EVALUATE YOUR SPECIFIC NEEDS BEFORE MAKING A PURCHASE. THINKSTOCK THE TASK, LOOKING BACK ON IT NOW, WAS PRETTY MUCH INSURMOUNTABLE—IMPOSSIBLE, EVEN. AS THE FORMER CO-CHAIR OF THE TOOL AND EQUIPMENT COMMITTEE FOR THE NATIONAL AUTOMOTIVE SERVICE TASK FORCE (NASTF), DONNY SEYFER HEARD THE QUESTION ALL THE TIME, FROM HIS FELLOW SHOP OWNERS, FROM REPAIR TECHNICIANS, EVERYONE: HOW DO YOU PICK THE RIGHT SCAN TOOL? SEEMED LIKE A SIMPLE QUESTION, HE THOUGHT, SIMPLE ENOUGH THAT NASTF SHOULD BE ABLE TO PROVIDE A RESOUNDING, CLARIFYING ANSWER TO THE INDUSTRY. SO, SEYFER’S TASK BECAME JUST THAT: CREATE A MATRIX THAT WOULD ALLOW SHOPS TO PICK THE CORRECT SCAN TOOL BASED ON THEIR RESPECTIVE WORK-MIX NEEDS. SEYFER FINISHED THE PROJECT IN 2012—OR, REALLY, HE SAYS, HE “ENDED” THE PROJECT. “WE WERE AWARE OF IT GOING IN, BUT THE PROBLEM WAS THAT IT WAS ESSENTIALLY IMPOSSIBLE TO EVER BE DONE WITH IT,” HE SAYS. “THERE ARE HUNDREDS OF TOOLS OUT THERE, AND THEY’RE CHANGING ALL THE TIME WITH NEW UPDATES AND SOFTWARE. IT’S SOMETHING THAT COULD NEVER BE FINISHED.”

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THE SCAN TOOL MATRIX THE MATRIX THAT SEYFER HELPED CREATE WITH NASTF, OFFICIALLY CALLED THE “VEHICLE MANUFACTURER SERVICE INFORMATION MATRIX,” HELPS TO PROVIDE DETAILS ABOUT OEM SERVICE INFORMATION, TOOLS AND TRAINING MATERIALS. IT CAN BE FOUND ON THE NASTF WEBSITE. STILL, SEYFER, OWNER OF SEYFER AUTOMOTIVE INC. IN WHEAT RIDGE, COLO., SAYS THAT IT’S NECESSARY FOR EVERY SHOP TO GO THROUGH THEIR OWN SIMILAR PROCESS OF FINDING THE CORRECT DIAGNOSTIC EQUIPMENT TO EFFECTIVELY REPAIR TODAY’S VEHICLES. “HAVING [THE CORRECT DIAGNOSTIC SCAN TOOL] IS THE BIGGEST THING IN INCREASING EFFICIENCY AND COMPETENCY—WHEN YOU HAVE THE RIGHT ONE,” HE SAYS. “AND, NOT HAVING THE CORRECT ONE IS GOING TO BE YOUR BIGGEST HINDRANCE. “VEHICLES TODAY HAVE SO MANY DIAGNOSTIC AND REFLASHING NEEDS, AND YOU’RE ONLY GOING TO SEE MORE AND MORE.” RESEARCHING AND PURCHASING SCAN TOOLS CAN FEEL LIKE A DAUNTING TASK, BUT, AS SEYFER AND CARQUEST’S GEORGE LESNIAK HELP POINT OUT, THERE ARE SIMPLE STEPS EVERY SHOP CAN GO THROUGH TO ENSURE IT EQUIPS ITS TECHNICIANS WITH THE RIGHT DIAGNOSTIC EQUIPMENT. TEACH A TECH TO FISH: THE CHALLENGES LESNIAK IS THE CURRICULUM DEVELOPMENT MANAGER FOR THE CARQUEST TECHNICAL INSTITUTE. HE’S BEEN TEACHING AND WRITING COURSES FOR TECHNICIAN TRAINING FOR 14 YEARS, AND HE HAS PERSONALLY RUN THOROUGH TEST TRIALS ON THE PRODUCTS OF A NUMBER OF AFTERMARKET AND OEM SCAN TOOL PROVIDERS. HE KNOWS DIAGNOSTICS, AND HE SAYS THAT BEFORE ANY SHOP OWNER SEES A SCAN TOOL AS A “SILVER BULLET” OR A “QUICK FIX” TO THEIR DIAGNOSTIC DILEMMAS, THEY NEED TO ASK THEMSELVES ONE QUESTION: HOW MUCH TIME AM I WILLING TO INVEST IN LEARNING THE ADVANCED FUNCTIONS OF THE SCAN TOOL I PURCHASE? “TECHNICIANS WANT TO KNOW WHAT’S WRONG WITH THE VEHICLE THEY ARE TROUBLESHOOTING TODAY,” HE SAYS. “THIS IS WHY SCAN TOOLS WITH BUILT-IN DIAGNOSTIC TIPS AND TRICKS ARE SO POPULAR. I BELIEVE THIS IS A FUNDAMENTALLY WRONG APPROACH. REMEMBER THE OLD ADAGE, ‘IF YOU GIVE A MAN A FISH … .’ WELL, THE SAME HOLDS TRUE FOR TROUBLESHOOTING. IF YOU GIVE THE TECHNICIAN AN ANSWER, HE MAY FIX A CAR BUT IF YOU TEACH A TECHNICIAN HOW THE VEHICLE WORKS, HOW HIS DIAGNOSTIC EQUIPMENT WORKS AND HOW TO THINK FOR HIS OR HERSELF, THEY CAN FIX NEARLY ANYTHING.” BOTTOM LINE: A SCAN TOOL IS NOT A CRUTCH, LESNIAK SAYS, EVEN THOUGH MANY TECHNICIANS AND SHOPS LIKE TO USE IT AS ONE. AND THAT’S JUST ONE OF THE MANY CHALLENGES THAT THESE TOOLS PRESENT. HERE ARE FOUR OTHERS SEYFER AND LESNIAK SAY TO KEEP IN MIND: 1. NO STANDARDIZATION. DESPITE THE PENDING CHANGES WITH RIGHT TO REPAIR LEGISLATION, THERE IS NO UNIVERSAL, STANDARDIZED APPROACH TO DIAGNOSTICS RIGHT NOW, , SEYFER SAYS. AND BECAUSE OF THAT, THE MAJORITY OF SCAN TOOLS OPERATE AND ROUTE THROUGH THE VEHICLE’S COMPUTER SYSTEM DIFFERENTLY. THAT’S WHY CERTAIN SCAN TOOLS WORK—OR EVEN PARTIALLY WORK—ON CERTAIN VEHICLES AND NOT ON OTHERS. IT’S ANOTHER REASON TECHS NEED TO UNDERSTAND THE TOOL AND THE VEHICLE SYSTEM, LESNIAK SAYS.

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2. REVERSE ENGINEERING. BECAUSE AFTERMARKET TOOL MAKERS ARE NOT GIVEN COMPLETE VEHICLE INFORMATION, THEIR TOOLS MUST BE REVERSE ENGINEERED TO BE ABLE TO WORK, AND THAT OFTEN CAN LEAD TO MISSED CAPABILITIES. 3. NOTHING IS UNIVERSAL—EVEN IF IT CLAIMS TO BE. ONE OF THE MOST DIFFICULT THINGS FOR SHOPS IS TO WEIGH A TOOL’S CLAIMED ABILITY AGAINST ITS ACTUAL CAPABILITIES, SEYFER SAYS. SIMPLY PUT: THERE IS NO ONE TOOL THAT CAN DO EVERYTHING FOR EVERY VEHICLE, OR EVEN COME CLOSE. AND THAT BRINGS US TO ...

4. INFORMATION GAPS. WHETHER IT’S BECAUSE OF REVERSE ENGINEERING OR EVEN SIMPLY NOT BEING THE LATEST VERSION OF A TOOL, THE EQUIPMENT WILL HAVE INFORMATION GAPS. THE PROBLEM IS, LESNIAK SAYS, A SCAN TOOL ONLY SHOWS YOU WHAT IT CAN DO, NOT WHAT IT CAN’T—YET ANOTHER REASON TO UNDERSTAND THE VEHICLES YOU WORK ON, HE SAYS. HUNTING FOR ANSWERS: CHOOSING YOUR TOOL EVERY SHOP WILL HAVE DIFFERENT NEEDS AND USES FOR A SCAN TOOL, SEYFER SAYS, SO IT’S CRITICAL TO IDENTIFY YOUR FACILITY’S SPECIFIC NEEDS FROM THE EQUIPMENT. HE AND LESNIAK OUTLINED SIX STEPS FOR DOING THAT. STEP 1: LOOK AT WHAT YOU WORK ON. TAKE A LOOK AT YOUR WORK MIX, SEYFER SAYS. WHAT VEHICLES DO YOU WORK ON THE MOST? WHAT MAKES, MODELS AND YEARS DO YOU SEE MOST OFTEN? “THE MORE SPECIFIC AND ‘SPECIALIZED’ YOU CAN BE WITH WHAT YOU WORK ON, THE BETTER OFF YOU’LL BE,” HE SAYS. PICK YOUR 10 MOST WORKED-ON VEHICLES, LESNIAK SAYS, AND FIGURE OUT YOUR NEEDS FOR THOSE. STEP 2: LOOK AT WHAT YOU DON’T WORK ON. OF COURSE, A SCAN TOOL SHOULD BE ABLE TO HELP YOU BRING IN ADDITIONAL VEHICLES, JOBS, REVENUE AND, ULTIMATELY, PROFITABILITY, LESNIAK SAYS. “PEOPLE ASK ME ALL THE TIME, ‘WHAT SCAN TOOL SHOULD I GET?’” HE SAYS. “AND MY FIRST RESPONSE IS ALWAYS ASKING THEM, ‘WHAT DON’T YOU WORK ON?’ THEN I ASK, ‘WHY?’ USUALLY, THAT HELPS YOU IDENTIFY VEHICLES IN YOUR AREA YOU’RE MISSING OUT ON. FOR AN EXAMPLE, SEYFER AND HIS SHOP RECENTLY INVESTED IN EQUIPMENT TO PROPERLY DIAGNOSE JAGUARS, AS HE SAW MANY IN HIS AREA AND VERY FEW SHOPS THAT WERE TAKING ADVANTAGE OF IT. STEP 3: RESEARCH THE TOOLS. HERE’S WHERE SHOPS OFTEN GET DISCOURAGED, LESNIAK SAYS, BUT IF YOU HAVE THE PROPER APPROACH AND THE CORRECT VISION FOR YOUR SHOP’S WORK MIX (STEPS 1 AND 2), THEN YOU’VE ALREADY NARROWED IT DOWN QUITE A BIT. THERE ARE SIX THINGS TO CONSIDER: COVERAGE. WHAT DATA DOES THE TOOL COME WITH? WHAT SUBSCRIPTIONS? WHAT VEHICLES DO THOSE COVER? WHAT MAKES AND MODEL YEARS? SEYFER SAYS THAT, BECAUSE OF CHANGES IN VEHICLE DESIGN AND CAPABILITIES, NOT EVEN OEM TOOLS COVER ALL OF THEIR OWN VEHICLES. AND SOME ARE ABLE TO ACCESS MULTIPLE MANUFACTURERS. YOU NEED TO FULLY UNDERSTAND WHAT EACH TOOL IS CAPABLE OF READING. TRAINING/EASE OF USE. MOST AFTERMARKET TOOLS ARE EASY TO “PICK UP AND GO WITH,” LESNIAK SAYS. OEM TOOLS OFTEN COME WITH A STEEPER LEARNING CURVE FOR FIRST-TIME USERS. TRY TO GET A FEEL FOR THE TIME AND EFFORT IT WILL TAKE FOR YOUR STAFF TO MASTER THE EQUIPMENT, AND WHAT TRAINING THE MANUFACTURER OR PROVIDER OFFERS. COMPATIBILITY. SOME TOOLS CAN BE USED THROUGH A WINDOWS-BASED PC OR LAPTOP, AND SEYFER SAYS THAT OFTEN MEANS ONE SINGLE TOOL CAN WORK WITH A NUMBER OF DIFFERENT VERSIONS OF MANUFACTURER SOFTWARE TO PROVIDE A WIDE RANGE OF COVERAGE.

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TECHNICAL SUPPORT. SOME TOOL MAKERS AND VEHICLE MANUFACTURERS PROVIDE HOTLINES OF SORTS TO CALL FOR ADDITIONAL INFORMATION OR FOR DIFFICULT DIAGNOSES. UNDERSTAND WHAT EACH TOOL HAS TO OFFER. UPGRADES/UPDATES. AS PER SEYFER’S DILEMMA WITH HIS NASTF MATRIX, TOOLS ARE CONSTANTLY BEING UPGRADED AND UPDATED. HE SAYS TO RESEARCH THE COMPANIES YOU’RE CONSIDERING AND SEE WHAT THEY OFFER IN TERMS OF UPGRADES—NOT JUST FOR THE PURPOSE OF THE EQUIPMENT BUT ALSO TO SEE IF THEY CUT ANY DEALS ON UPDATING THE TOOL. COST. THERE’S GOING TO BE A LARGE DISCREPANCY IN PRICE BETWEEN TOOL MAKERS. THIS IS WHY UNDERSTANDING YOUR WORK MIX IS IMPORTANT TO GRASP THE VALUE OF THE TOOL. STEP 4: ANALYZE THE RETURN. THERE ARE A LOT OF WAYS TO TRY TO ANALYZE HOW VALUABLE A SCAN TOOL IS IN A SHOP. SEYFER LIKES TO SORT OF LOW-BALL THE RETURN AND ONLY COMPARE THE COST OF THE TOOL (INCLUDING SUBSCRIPTIONS AND UPGRADES) TO THE AMOUNT OF MONEY HE MAKES ON DIAGNOSTIC CHARGES. OBVIOUSLY, HE SAYS, THAT DOESN’T TAKE INTO ACCOUNT ANY IMPROVEMENTS IN EFFICIENCY, CAR COUNT, ETC. HE SAYS IT HELPS GIVE HIM AN ABSOLUTE MINIMUM THAT CAN SERVE TO DIRECTLY PAY OFF THE TOOL. STEP 5: DEMO THE TOOLS. LESNIAK SAYS TO BE WARY OF ANY COMPANY THAT ISN’T CONFIDENT ENOUGH IN ITS PRODUCT TO LET YOU HAVE IT FOR A FULL, ON-YOUR-OWN TRIAL PERIOD. “RECEIVING A DEMO FROM THEM IS NOT GOOD ENOUGH,” HE SAYS. “YOU NEED TO HAVE IT IN YOUR TECHNICIAN’S HANDS AND LET THEM BE ABLE TO SEE ITS FULL CAPABILITIES ON YOUR ACTUAL WORK MIX. TESTING THE TOOL ON YOUR OWN IS THE MOST IMPORTANT THING YOU CAN DO TO MAKE THE CORRECT DECISION.” STEP 6: IMPLEMENT THE TOOLS. ALTHOUGH THIS STEP MUST COME AFTER YOU SELECTED AND PURCHASED A TOOL, IT WILL ALSO HELP TO CONFIRM YOUR DECISION. DON’T JUST SIMPLY BUY DIAGNOSTIC EQUIPMENT AND HAND IT OFF TO THE TECHNICIAN. CREATE PROCESSES AND SYSTEMS FOR YOUR SHOP TO USE IT CORRECTLY, SEYFER SAYS, AND MAKE SURE TO MARKET YOUR CAPABILITIES. KEEP IT SIMPLE LESNIAK AND SEYFER BOTH FEEL THAT CHOOSING A SCAN TOOL FOR YOUR SHOP CAN BE A DAUNTING TASK. THE IMPORTANT THING TO REMEMBER, SEYFER SAYS, IS THAT YOU NEED TO FIND THE BEST FIT FOR YOUR BUSINESS—NOT JUST THE FLASHIEST, MOST EXPENSIVE EQUIPMENT (OR THE MOST AFFORDABLE, FOR THAT MATTER).

GET AS MUCH INFORMATION AS YOU CAN, LESNIAK SAYS. TALK WITH OTHER SHOP OWNERS, TALK WITH YOUR VENDORS, ASK ABOUT IT IN 20 GROUP MEETINGS, ASSOCIATION GATHERINGS, ON MESSAGE BOARDS—ANYWHERE YOU CAN. THERE’S PLENTY OF INFORMATION ONLINE ABOUT EACH TOOL AND IATN, THE EQUIPMENT AND TOOL INSTITUTE (ETI), NASTF AND OTHERS HAVE DETAILED INFORMATION. IN THE END, THOUGH, LESNIAK SAYS TO TRY TO MAKE THE PROCESS AS SIMPLE AS YOU CAN. “THERE’S NO ONE ANSWER FOR ANY SHOP,” HE SAYS. “BUT, IF YOU DO YOUR RESEARCH AND TEST THE [SCAN TOOLS] OUT BEFOREHAND, YOU CAN MAKE IT A WHOLE LOT EASIER ON YOURSELF.”

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Bulletin TB-80017 December, 2009

On Board Diagnostics Part II Gary Stamberger – Training Director Magnaflow Exhaust Products As promised from last month, more on OBD. Refer to our Website, Magnaflow.com for archived Bulletins. (http://www.magnaflow.com/07techtips/techbulletins.asp) Data Stream Referred to as Current Data or Live Data, this information is available to the technician using a Scan Tool. The number of PIDS (Parameter Identification) available at any given time will depend on a couple of different factors. The particular vehicle (Manufacturer) involved will have the greatest influence on the amount of data available. Followed by the type of Scan Tool used and whether you are viewing the data on the Global OBD II side or Manufacture Specific, aka Enhanced Mode. (Figure 1) Most Scan Tools will have options for viewing the data in different formats such as digital or graphing mode. Graphing can be particularly useful when looking at Oxygen Sensor activity. (Figure 2) The data available will consist of inputs and outputs, calculated values and system status information.

Viewing data and becoming proficient at recognizing problem areas is one of the skills we spoke of in last months Bulletin (TB-80016). Part of any training on a particular tool is the repetitive process of using it over and over until you begin to recognize when certain data doesn’t look right. This process will then lead you toward a problem area where further testing will reveal the fault. You can not recognize bad data until you have looked at enough good data. One item to be aware of is the practice of substituting good data values for suspect ones. Due to something called Adaptive Strategy, when the PCM suspects that a particular input may not be reporting accurately, it will substitute a known good value for that sensor and run the vehicle on learned values. This will only show up in Enhanced Mode as Global OBD II will always display actual values. This should not deter you from viewing in Enhanced Mode. It has always been my practice to look at codes and data in both modes.

FIGURE 1

FIGURE 2

Freeze Frame Freeze frame is a “snap shot” of data taken when a code is set. This can be very valuable information as it allows the technician an opportunity to duplicate the conditions under which the trouble code was recorded. The number of freeze frame events recorded and viewable by the technician will again depend on the vehicle and scan tool being used. Early systems could only store one batch of information, if more than one code was recorded we would typically only be able to view the Freeze Frame for the last code set. Changes in both OBD and Scan Tool technology have allowed us to have multiple sets of information available for multiple codes set. One exception is that of Misfire. Misfire codes and subsequent data take precedent and will overwrite any previous freeze data stored. Be aware that all freeze frame information is lost when codes are cleared.

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FIGURE 3

FIGURE 4

Courtesy Toyota

Monitors Monitors, also referred to as Readiness Indicators are considered the single most comprehensive change that came with OBD II. CARB and the EPA recognized that a vehicle started polluting long before the PCM recognized a fault, set a code and illuminated the MIL. Early OBD systems did not have the capability to recognize degradation of components or systems. Today’s OBD II system is designed to recognize when a vehicle could potentially exceed its designed emission standard by a factor of 1.5. It does this through a series of system Monitors.

During normal operation the PCM will conduct certain tests to gauge the operational health of a particular system or component. The Monitors operate in two categories, Continuous and Non-Continuous. As you can probably guess the Continuous Monitors run, well, continuously. They are Misfire, Fuel System and Comprehensive Component. Non-Continuous consist of Catalyst, Evaporative, Oxygen Sensor, Oxygen Sensor Heater, EGR Monitor and more. These require a very specific Drive Cycle (Figure 4) that will meet all the criteria necessary for a complete test. Scan Tools will have a Monitor Status screen that indicates if the Monitors have run to completion. (Figure 3) Next to each component or system it will indicate “Ready” or “Not Ready”, “Complete” or “Incomplete”. If the vehicle is not equipped with a certain system the screen will indicate “Not Supported” or “Not Available”.

When one or more indicators read Not Ready or Incomplete, it is an indication that codes have been cleared recently, either with a scan tool or loss of power to the PCM such as battery disconnect. If there is no history of either of these events occurring this is an indication of the PCM intermittently loosing power or it is rebooting which could be an internal problem. It is commonly known that the Catalyst and Evaporative System Monitors are the hardest to run to completion.

Many states have moved to an OBD system test for Emission Testing in place of tail pipe testing for vehicles 1996 and newer. California is considering this transition as we move into 2010 (No date has been set for implementation). The test includes checking for proper location of DLC (Data Link Connector), bulb check of MIL, no MIL when vehicle is running, no codes in system and all the Monitors have run to completion.

Monitors are a key component because they are a direct indication of whether the OBD system had been tampered with prior to Inspection.

The USEPA and CARB authorities have generally found that OBD II systems are more effective in detecting emission-related malfunctions on in-use vehicles compared to existing Inspection and Maintenance (I/M) tailpipe testing procedures. Current Smog Check data indicates that vehicles are more likely to fail an OBD II-based inspection than the required tailpipe emissions test. With the reduced testing times (10 mins. for OBD vs. 20 mins. for tail pipe) and cost savings in equipment it’s not beyond the realm of possibility that states currently having none or minimal Inspection Programs may consider adopting an OBD Emissions Testing program. These programs have proven to create a healthy environment and also a healthy bottom line for repair shops.

Cleaning up the environment…one converter at a time Gary

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Foreign Service Trouble codes and their descriptions can be a mixed blessing. A stored code may not seem to match the symptoms, and a poorly worded or vague description may confuse rather than clarify.

I

deally, every vehicle coming into your shop would have obvious symptoms.

Furthermore, its computer would have stored a valid trouble code that points you to the root of the vehicle’s problem(s). Then you would replace a part and make tons of money.

The real world, of course, is very different. dmarinucci@motor.com Sometimes a vehicle shows up with no symptoms or trouble codes. If a DTC has been set, sometimes it just doesn’t make sense—doesn’t seem relevant. Then, to make matters worse, we may have to coax a meaningful vehicle history out of the car owner. Some jobs simply demand more homework and testing that others do. In turn, a job may require old-fashioned patience. Here’s an example I encountered last year.

I was doing homework at my buddy’s shop when a pristine 1996 Honda Accord arrived. An existing customer had referred the Accord’s owner to the shop. Its Check Engine light was on and its PCM had set a P0715 trouble code (transmission speed sensor). Although the car had 290,000 miles on it, every detail about it suggested that it had received lots of care. So we weren’t surprised when the guy produced a thick folder of service records.

Among other details, his receipts showed that a shop back home (out of state) had been changing the trans fluid about every 24 months. That probably explained why the car still had its original, four-speed automatic transaxle.

The man said the only symptom he noticed was something that had developed over the last six months: a noticeable delay when he shifted the trans from Reverse into Drive.

But this delayed engagement occurred only in the morning when the car was stone cold. Afterward, it performed normally. Tony, This is an example of the clean, consisone of the shop’s technicians, had tent AC voltage waveform the Accord’s already retrieved and cleared the mainshaft speed sensor produced during the road test described in the text. code. Then he checked the fluid Screen capture: Dan Marinucci

Dan Marinucci

12

January 2015

level and performed a brief road test. No symptoms or codes appeared at this time.

Next, we double-checked Honda’s definition of the DTC. Its description of P0715 was “a problem in the mainshaft speed sensor circuit.” First of all, problem could mean several possibilities. Second, we guessed that this description included the speed sensor itself. Third, we had seen some speed sensors fail on higher-mileage Honda transmissions.

Fourth, we had the issue of the delayed engagement when cold. This symptom usually means that transmission seals are beginning to leak. Leaking seals, in turn, mean a pending transmission failure.

Furthermore, we realized that this Accord could have several problems. On one hand, the owner had an impressive collection of detailed maintenance records. On the other hand, the car’s odometer still read 290,000 miles. Suppose the shop replaced the transmission and that P0715 code reappeared? Wow, that would be embarrassing.

To me, the circumstances called for additional road-testing. Hopefully, the car would show some meaningful symptoms and possibly reset the DTC within a reasonable amount of time. Maybe the speed sensor signal was weak or intermittent. Experience has taught me that erratic speed sensor signals could wreak havoc with a transmission computer’s decision-making process.

Meanwhile, the shop was very busy. The only available scan tool didn’t show us any mainshaft speed sensor data on this Accord. Fortunately, I had my oscilloscope with me. We checked a schematic for the speed sensor and found that the sensor contained a wire coil. A two-wire harness connected this sensor to the PCM. I explained to Tony that these details often suggested an analog speed or position sensor that produced an AC voltage signal. Thankfully, the PCM was located on the right front floor at the base of the firewall. So it would be fairly easy to scope the sensor during a road test.

First, Tony drove the Accord around the neighborhood while I rode shotgun with my scope connected to the speed sensor input to the PCM. Then we swapped seats so he could practice scope-

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Brandon Steckler

testing. The mainshaft speed sensor produced a clean, consistent AC wave that never faltered.

Eventually, the Check Engine light turned on again while the speed sensor was working fine. At least now we knew that a goodlooking signal was reaching the Line-graphing of mainshaft speed is on the right, with countershaft speed on the left. This PCM; that should rule out a senwas captured on a 2002 Acura TL automatic transaxle with a Snap-on MODIS. Note that calcusor or wiring failure. lated vehicle speed on the left increases smoothly and steadily. But clutch slippage caused the Finally a vital symptom ocmainshaft speed on the right to increase rapidly and abruptly. curred on the way back to the shop. We began hearing telltale sounds simplify once again, the mainshaft is the and mainshaft 3rd gear are on the mainof a slipping transmission; engine speed input shaft to the entire transaxle; the shaft. When a tired old 3rd clutch begins was “spinning up” during light accelera- countershaft, which is its output shaft, slipping, it allows the mainshaft speed to tion. What’s more, the car’s tachometer drives the transaxle’s differential.) rise above its normal range (compared to confirmed what we heard because it Although both speed sensors produce the countershaft). Then the PCM recogshowed that rpm was flaring up in 3rd AC voltage signals, these signals operate nizes this abnormally high mainshaft gear. Now we had an additional clue at different frequencies. The PCM con- speed and sets the DTC. that the transmission was failing. stantly monitors both signals, computing Before I wrap up for this month, note Back at the shop, we had another sur- vehicle speed from each one. What’s that troubleshooting newer Hondas is prise: The same DTC, P0715, was the more, it compares the “calculated” vehi- easier for several reasons. First, you’ll only code present. Our extensive scope cle speed of the mainshaft to that of the find that more trans trouble codes are test suggested that the speed sensor and countershaft. According to Honda, the available. Second, the codes are more its circuit were okay. But for some rea- computer tolerates some variation be- detailed; for example, you’re likely to see son, the PCM didn’t agree. Computer tween them. However, the PCM sets a specific “ratio error” DTC set for the failure on these Hondas wasn’t very com- DTC P0715 whenever it detects an ab- failing clutch or gear range. mon. What was going on here? normal difference between these two calThird, you’re more likely to be able to We retrieved the info on the P0715 culated vehicle speed inputs. On some read vital transaxle data with a capable code again and studied it closer than we Honda automatic transaxles, then, our scan tool. For instance, one Honda spehad earlier that morning. Yes, Honda’s dastardly DTC could appear even though cialist described setting up his scan tool information clearly identified this DTC the mainshaft speed sensor and its circuit to line-graph just two PIDs—mainshaft as “Problem in Mainshaft Speed Sensor tested okay. If we had patiently read speed and countershaft speed. Now Circuit.” And yes, this still sounded like through the DTC description that morn- suppose you line-graphed calculated vean electrical issue. As I continued read- ing, we probably would have caught hicle speed for each of these during a ing, I realized that the code description these vital details. road test on a healthy transmission. In really didn’t match its definition.

Later I learned that techs at one of my that case, the calculated mph readings Here it would help to recap something favorite Honda shops call DTC P0715 the for the mainshaft and countershaft I covered last month. Popular four- or “death code” for tired automatic transmis- would match each other throughout five-speed Honda automatic transaxles ac- sions. By the way, my pal got an authoriza- each gear range. Remember, normal tually resemble a common manual gear- tion, installed a remanufactured trans and fluctuations in these readings occur each box—they have a mainshaft and counter- the Accord owner is pleased as punch. time the transaxle shifts gears. Refer shaft laid out just like those in a stick-shift I mentioned earlier that the Accord’s back to my earlier example of the sliptrans. To grossly simplify, Honda has cre- transmission was slipping in 3rd gear. Ac- ping 3rd clutch. There, a slipping 3rd ated automatic transaxles by adding the cording to Honda’s power flowchart, the clutch would cause a gross speed differnecessary hydraulics—including clutch 3rd clutch should apply in 3rd gear. Basi- ence between the two shafts in 3rd gear. packs—to a manual trans layout. cally, power flows from the torque conWhen I was a kid back in Catholic Apparently, the Accord’s PCM moni- verter, through the mainshaft and into the school, the nuns repeatedly emphasized tors vehicle speed from two sources with- 3rd clutch. Then the applied 3rd clutch that patience was a virtue. If that’s really in the automatic transaxles. One is a speed should drive mainshaft 3rd gear, which true, then virtuous MOTOR readers will sensor on the mainshaft, the other is a should send the power through counter- always peruse the entire DTC descripspeed sensor on the countershaft. (To shaft 3rd gear. Yes sir, both the 3rd clutch tion before taking action. Amen!

January 2015

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MAP Sensor This issue I am going to explain the MAP (Manifold Absolute Pressure), MAF (Mass Air Flow), and IAT (Intake Air Temperature sensors and their func ons. Stock Fiero engines have MAP and IAT sensors but no MAF. Most popular engine swaps do u lize MAF sensors so I will cover those as well.

Some engines only u lize a MAP or Manifold Absolute Pressure sensor. The MAP sensor has 5 volt reference and ground inputs and in turn outputs a voltage signal between 0 and 5 volts depending on the pressure it senses. This sensor is responsible for measuring the pressure in the intake manifold rela ve to atmospheric pressure. When the pressure it senses is lower than atmospheric pressure (vacuum), the sensor will output a lower voltage. As the pressure it senses rises to match atmospheric pressure (vacuum drops), the voltage output of this sensor rises. This sensor also doubles as a barometric pressure sensor. When you turn the key on before star ng the engine, the ECM takes the reading off the MAP sensor and uses that to calculate barometric pressure. The ECM uses barometric pressure as the basis for calcula ng fuel and spark delivery to the engine.

When the engine is started, the ECM uses the MAP sensor readings to determine engine load. This is the primary sensor it uses to determine fuel and spark delivery to the engine. The MAP sensor reading is factored in with engine RPM to calculate volumetric efficiency. This is known as Speed Density (engine speed and density of the air charge). Volumetric efficiency (VE) is the term used to describe the amount of air an engine is inges ng vs. the amount of air it can actually hold, expressed in a percentage. If the engine is inges ng the maximum amount of air it can hold, then that engine is considered to be opera ng at 100% VE. Most naturally aspirated engines never see 100% VE; but engines using specially‐tuned intake manifolds can accomplish this. Of course this can also be accomplished and exceeded with a turbo or supercharger by adding boost. Most naturally aspirated engines typically see up to 80‐90% VE without a tuned intake design.

Obviously if there is a problem with the MAP sensor, or the vacuum/pressure readings it is ge ng are not accurate, this is going to greatly affect the way the engine runs. GM MAP sensors aren’t easily prone to failure, but I have seen them fail if exposed to great pressures such as what could occur if the engine backfired thru the intake. The most common situa on that I see that can cause issues with the MAP sensor is a vacuum leak. Any kind of vacuum leak will cause the pressure levels the MAP sensor sees to be lower than expected. This tends to cause the Air/Fuel mixture to go rich (because the ECM thinks the engine is under a load).

On most OBD1 applica ons, there are two trouble codes associated with the MAP sensor. A code 33 will set if the MAP sensor output voltage is higher than expected (indica ng low vacuum) and a code 34 will set if the MAP sensor output voltage is lower than expected (indica ng high vacuum). As with any trouble code detected, you should not assume the presence of either one of these codes indicates the MAP sensor itself is bad. All electrical and vacuum connec ons to the MAP sensor should be verified before replacing the part. To give a couple examples of what to look for should you get a code 33 would be a vacuum leak, mechanical issue with the engine causing very low vacuum levels, or an electrical problem between the sensor and ECM. If you are ge ng a code 34 you should look for a collapsed or blocked vacuum line going to the MAP sensor or electrical problem between the ECM and sensor. Normal output voltage of a MAP sensor should be about 4.5 volts or so with key on, engine off; and less than 1.5 volts with engine running at idle. At full thro le you should see MAP output voltage above 4 volts. If there is a fault with the MAP sensor or the readings the ECM is ge ng from it are incorrect, the engine will most likely run very poorly, lack power, hesitate, backfire, or surge. Basically overall engine opera on will most likely be unstable.

The stock MAP sensor used on all non‐supercharged and non‐turbocharged engines is what as known as a 1‐bar MAP sensor. This means the sensor is designed to read up to 1‐bar of atmospheric pressure difference. Applica ons using a turbo or supercharger may have a 2‐ or 3‐bar MAP sensor. A 2‐bar MAP sensor will read up to 2‐bars of atmospheric pressure difference, and a 3‐bar will read up to 3. But all of these sensors must s ll operate within the same voltage output specs as a 1‐bar. So in order to accomplish this, the output voltage must be scaled accordingly. This means the output voltage of a 2‐bar map sensor with the key on and engine off is going to be somewhere around 2.5 volts. You cannot mix and match 1, 2, and 3 bar MAP sensors. The computer must be programmed to work with whatever type of MAP sensor you are using, or the fuel and spark delivery will not be correct (and trouble codes may set).

IAT Sensor If present, the Intake Air Temp (IAT) sensor (aka: MAT – Manifold Air Temp) is used by the ECM to tell it the temperature of the air coming into the engine. The ECM uses this input to aid in the calcula on of fuel and spark delivery. The IAT sensor is a simple thermistor which means its resistance changes based on its temperature. The ECM supplies the IAT sensor with a ground and a

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reference signal. The IAT sensor pulls down (towards ground) the reference signal based on temperature and the ECM looks at this to calculate temperature. High resistance equates to less reference voltage pull down which the computer interprets as low temperature while low resistance equates to more reference voltage pull down which the computer interprets as high temperature. The actual amount of impact this sensor has on engine opera on is rela vely minor, depending on programming.

Most stock programming I have looked at doesn’t adjust fuel or ming much at all based on IAT sensor readings. Most TBI‐type fuel injec on systems do not use an IAT sensor.

On most OBD1 applica ons, two trouble codes are associated with the IAT sensor. A code 23 indicates the intake air temp reading is lower than expected. If this code is present, before replacing the sensor you should check for an open circuit to the IAT sensor wiring. A code 25 indicates the intake air temp reading is higher than expected. If this code is present, check IAT signal wire for a short to ground before replacing the sensor. If either code is set, or there is a problem with the IAT sensor, it is unlikely you may no ce any running change in the engine. However, in some cases (depending on computer programming) if the ECM is not ge ng the correct reading from the IAT sensor, it may be altering the spark advance or fuel delivery to the engine incorrectly which may cause some drivability issues such as spark knock (detona on), loss of power, or exhaust odor because of incorrect fuel mixture.

The IAT sensor can be tested using a simple ohm meter. In order to test this sensor, unplug it from the wiring harness and measure the resistance across its two terminals. The temperature vs. resistance chart is below… °F 210 160 100 70 40 20 0

‐40

°C 100 70 38 20 4 ‐7 ‐18 ‐40

OHMS 185 450 1,800 3,400 7,500 13,500 25,000 100,700

MAF Sensor The MAF or Mass Air Flow sensor (if present) is the main sensor used by the ECM to determine Fuel Delivery. MAF sensors usually consist of a tube that may or may not contain passages but all types contain some kind of sensing element. The MAF sensor is usually installed in the induc on system close to the engine or might even be part of the thro le body. Most MAF sensors calculate airflow depending on temperature changes detected by its sensing elements using its internal circuitry. In turn the sensor outputs a signal to the ECM that is used to determine airflow and calculate engine load. Most modern MAF sensors output a varying frequency signal which can only be accurately measured using specialized tes ng equipment, such as a lab waveform scope.

Some computer systems u lizing MAF sensors tend to use this sensor as the main input for calcula ons that determine fuel and spark delivery to the engine. However, in some pre‐OBD2 and early OBD‐2 applica ons where both a MAP and MAF sensor are present, the computer may be using the MAF sensor to only determine fuel delivery while it uses the MAP sensor to determine spark advance. Yet, in other applica ons (such as later OBD‐2), the MAP sensor is primarily used as a backup should the MAF sensor fail; while the MAF sensor is the primary device used by the ECM to calculate fuel and spark delivery to the engine. To further complicate ma ers, there are applica ons (usually LS1 car and Vortec Truck) where both the MAF and MAP are used to determine fuel delivery. These systems rely on the MAP sensor to supply quickly changing informa on used for accelera on enrichment calcula ons where the MAF sensor is used for less dynamic fuel delivery modes. Most modern MAF sensors also contain an IAT sensor.

Like the MAP sensor, if a trouble code sets for a MAF sensor error, some things must first be checked before replacing the sensor.

Leaks in the air induc on system or intake manifold can cause the MAF sensor to produce false readings, so can faulty wiring.

MAF sensors that output a frequency signal to the ECM can also give false readings if they are exposed to electromagne c interference such as what is generated by the igni on system. Output voltage and frequency specs differ depending on applica on and type of MAF sensor used, so refer to the correct service manual informa on for your specific tes ng procedures.

Back to Tech Page

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Diagnostic Dilemmas: The Pressures of Intake Manifold Vacuum Tests ■Emissions ■Engine

by Gary Goms - Sep 1, 2006

Several years ago, a retired school teacher brought in a 1994 Chevrolet S-10 Blazer that had developed an intermittent rough idle condition. Although a rebuilt engine had been installed a year before, and all of the wiring and vacuum hoses looked as if they were in factory condition, I took nothing for granted.

An ignition scope and compression test yielded no result and neither did spraying the manifold gaskets with aerosol carburetor cleaner. When I connected a vacuum gauge to the intake manifold, the needle would jiggle ever so slightly when the engine began misfiring. A few moments later, the vacuum reading would stabilize and the engine would idle very smoothly. I suspected a broken valve spring, but removing the valve covers on this particular engine is difficult and time-consuming due to accessory interference.

With these thoughts in mind, I began devising a diagnostic strategy that would tell me which bank was misfiring and, with a little luck, which cylinder was misfiring.

Vacuum Terminology Intake manifold vacuum analysis can be a little tricky because the conventional term “intake manifold vacuum” is a technical misnomer. Technically speaking, the intake manifold must contain enough liquid fuel and air to support combustion, so what we have is not a complete vacuum, but an atmospheric “pressure differential” between the inside and outside of the intake manifold. A more current term refers to the pressure inside the intake manifold as Manifold Absolute Pressure or “MAP.” As currently used, the terms “pressure differential,” “MAP” and “intake manifold vacuum” refer to the difference between atmospheric and intake manifold pressures.

Atmospheric Pressure Atmospheric pressure is about 14.7 pounds per square inch of pressure at sea level. Atmospheric pressure at sea level will also support a column of liquid mercury (Hg) 29.92” in height. Since local weather conditions may cause atmospheric pressure to vary from standard, the current reading is usually referred to as “barometric pressure” or “baro.”

When testing manifold vacuum, it’s important to remember that if an engine idles at 22” Hg at sea level, it will idle at about 17” Hg at 5,000’, 14” Hg at 8,000’ and 12” Hg at 10,000’ altitude. Variations from the calculated standard, of course, are the weather conditions, the engine design, and how well the engine management system adjusts spark advance and air/fuel mixture to correspond to a change in barometric pressure.

Operating Vacuum Because atmospheric and intake manifold pressures begin to equalize as the driver opens the throttle plate, intake manifold vacuum is normally measured at idle speed. At wide-open throttle (WOT), atmospheric and manifold pressures become nearly equal as air rushes in to fill the engine’s cylinders.

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At its most basic level, intake manifold vacuum testing consists of connecting a vacuum gauge to a port tapped into the intake manifold. From that point, testing intake manifold vacuum becomes a little more problematic because a number of engine design issues like variable camshaft timing, tuned intake systems, high valve overlap, and, of course, turbocharging or supercharging may affect intake manifold vacuum readings.

In other cases, a variation from normal values may indicate the problem itself, which might be a stuckopen EGR valve, a bent or burned intake or exhaust valve, worn camshaft lobe, broken or weak valve spring, a broken cam follower or rocker arm, incorrect camshaft timing, incorrect spark timing, clogged catalytic converter, burned piston, leaking intake gasket or vacuum hose, or rich or lean air/fuel mixtures.

Engine Management Strategies With the exception of electronically controlled valve train systems, the idle speed of all other fuel-injected spark ignition engines is managed by a precision-machined throttle plate mounted in a precision bore.

When adjusted correctly, the throttle plate will allow the engine to idle at a base speed of about 500 rpm.

Due to the volume of air flowing around the throttle plate to maintain idle speed, the sea-level pressure differential or “vacuum” is normally reduced from 29.5” Hg to about 18” to 22” Hg at idle on a welltuned engine.

At the most basic level, peak cylinder pumping efficiency, idle speed power output and combustion efficiency go hand-in-hand with peak intake manifold vacuum. Complete combustion of the air/fuel mixture is achieved when the fuel mixture is ignited a few crankshaft degrees before the piston reaches top dead center (TDC) and before maximum cylinder compression pressure is reached. The base spark timing is normally advanced to allow time for a flame front to propagate from the spark plug into the combustion chamber. As the cylinder reaches maximum compression, the rate of combustion increases because the compressed air/fuel molecules ignite very rapidly.

If the spark occurs too early in the combustion cycle, the combustion rate slows down because the cylinder hasn’t reached maximum compression. Consequently, a misfire develops because the loosely packed air and fuel molecules fail to support combustion. If the spark occurs too late in the combustion cycle, the slowly burning fuel mixture fails to exert maximum pressure against the piston.

Most mechanically managed engines ignite the fuel between zero and 12 degrees of base spark timing before top dead center (BTC) at idle speed. In general, maximum intake manifold vacuum is achieved just as the spark timing is advanced to the point of misfire. As the spark is retarded, idle quality improves because ignition is occurring as maximum compression pressure is achieved in the combustion chamber.

Further retarding spark timing reduces intake manifold vacuum because less fuel is efficiently burned, which reduces the pumping efficiency of the engine’s pistons and cylinders.

Similarly, the air/fuel mixture reduces intake manifold vacuum when it varies from a stoichiometric mixture to a rich or lean mixture. In the heyday of the mechanically managed engine, skilled mechanics carefully adjusted spark timing and air/fuel ratios to balance the highest vacuum reading against the smoothest idle quality. In many cases, a skilled technician armed with an accurate vacuum gauge achieved optimum spark timing by advancing the spark timing into misfire and then retarding several inches of mercury to achieve a smooth idle.

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To adjust the idle air/fuel mixture, the technician would adjust the mixture screw to achieve maximum intake manifold vacuum and then open the adjustment screw one-quarter to one-half turn more to compensate for temperature and barometric pressure changes. In most cases, fuel economy would improve because the carburetor’s power enrichment system, which normally begins to open at 6.4 to 8.5” Hg, remains closed with the higher vacuum achieved by precision tuning.

Electronic engine management systems essentially follow the same strategies, but with much tighter parameters. Most, for example, advance the spark timing and lean the fuel mixture to the point of misfiring at idle speeds. In most cases, highly efficient, electronically controlled engines produce a slightly higher vacuum reading than do mechanically controlled engines.

Vacuum Instrumentation Intake manifold vacuum can be measured with a mechanical gauge, electronic pressure transducer, or through the engine management system via a diagnostic scan tool. Compared to consumer-grade instruments, a professional-quality mechanical vacuum is accurate, responsive and produces repeatable results. Responsiveness is a particularly important feature because, to produce relevant data, the gauge must detect minor vacuum fluctuations caused by leaking valves and other reciprocating engine parts.

Similarly, electronic vacuum transducers that connect to lab scopes and graphing or digital multimeters must have enough sensitivity to display minor variations in manifold vacuum. A digital multimeter, for example, can be set to display minimum and maximum values. Although lab scopes and graphing multimeters can display variations in manifold vacuum as a voltage trace or a graph, While scan tools usually display barometric, MAP and/or vacuum in numerical values, the update rates are usually too slow to be useful in diagnosing vacuum irregularities caused by reciprocating parts. In addition, the software strategies and hardware differ widely among vehicle applications. Speed density systems, for example, use a MAP sensor to measure both the baro and MAP. With the key on and engine off, the baro input informs the PCM how weather and altitude pressure changes will affect the MAP input. After the engine starts, the baro input becomes a value upon which the MAP reading is based. This strategy prevents the PCM from seeing a 14” Hg MAP input as an out-of-parameter reading at an altitude of 8,000’. Some mass air flow (MAF) sensor-equipped vehicles may use a separate baro sensor to adjust for weather and altitude changes. In other cases, vehicles equipped only with a MAF sensor will calculate barometric pressure by measuring the air flow into the engine at a specific engine speed, throttle opening and intake air temperature reading and storing that value in the PCM’s keep-alive memory as a barometric pressure reading.

Scan Tool Vacuum Diagnosis Electronically managed engines react to vacuum leaks differently than mechanically managed carbureted engines. Assuming a carbureted engine is adjusted to a stoichiometric idle mixture, a vacuum leak will reduce intake manifold vacuum because the airflow is no longer controlled by the throttle plate and also because the excess airflow leans out a stoichiometric fuel mixture.

On the other hand, electronically managed engines add an idle speed control (ISC) or idle air control (IAC) device to the throttle assembly to provide a more accurate control of idle speed. While the so-called 3

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“base” or “minimum” idle speed is controlled by the throttle plate, the curb idle speed is controlled by a motor or solenoid that allows additional intake air to bypass the throttle plate. Since minor vacuum leaks increase idle speed on closed-loop fuel systems, the PCM commands the ISC to reduce air flow into the intake manifold. To illustrate, the ISC or IAC “count” for a typical General Motors vehicle ranges between 20 and 30. A major vacuum leak would force the PCM to force the IAC count to zero.

In addition, air from a vacuum leak will increase fuel trim readings because the PCM will add fuel by increasing fuel injector pulse width (IPW) to maintain a stoichiometric air/fuel ratio. Last, if a manifold gasket leak causes a lean misfire to occur on one cylinder, most OBD II systems will record a misfire for that cylinder.

The single exception to the PCM increasing fuel trim readings is when a sticking EGR valve causes a vacuum leak by allowing exhaust gases to dilute the air/fuel mixture present in the intake manifold. The effects of a stuck-open EGR are problematical because, on the one hand, chemically inert exhaust gas dilutes the air and fuel in the manifold and reduces the power output and pumping efficiency of the engine. Speed density systems often react to the reduced intake manifold vacuum by increasing IPW because the MAP input falsely indicates an increased engine load.

In contrast, MAF sensor-equipped engines sense a decreased intake air flow through the MAF sensor and may react by reducing IPW. The most important issue with EGR contaminating the air/fuel mixture of speed density and MAF-equipped engines is that vehicles may have different operating strategies programmed into their engine management systems to deal with stuck-open EGR valves.

To illustrate, I’ve had one Chrysler in which an EGR valve with a missing pintle caused only a minor rough idle condition. In contrast, a small piece of carbon trapped under the EGR pintle of a General Motors 4.3 engine can cause an extremely rough idle or engine stall.

The logic revolves around how the PCM reacts to a stuck EGR valve.

In the case of the Chrysler, the PCM may let the authority of the oxygen sensor override the authority of the MAP sensor. With the GM product, the exact opposite might be true.

Vacuum Gauge Analysis Any vacuum reading, whether measured mechanically or electronically, should remain steady at idle and represent a typical value for the engine configuration and operating altitude. During cranking at closed throttle, an engine should generate at least 3 to 5” Hg of manifold vacuum. If cranking vacuum isn’t present, the engine might have a broken timing belt or chain.

If the vacuum reading is low, the base ignition timing may be retarded, one or more camshafts might be retarded, or the EGR valve might be sticking open. If the intake manifold vacuum is higher than normal, the base ignition timing or intake camshaft timing might be too far advanced. If the gauge fluctuates, one or more cylinders are leaking vacuum through a reciprocating part like a leaking intake or exhaust valve or burned piston.

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Manifold vacuum should increase slightly as the engine is held at 2,500 rpm at steady throttle. If the vacuum is the same or decreases, the exhaust might be restricted. At snap throttle, the vacuum gauge should plunge to zero and then increase at least 25% above idle values as the throttle is snapped closed. If an increase isn’t noted, the engine may have worn piston rings or valves.

The Blazer Wrap-Up I almost forgot about the Chevy S-10 Blazer with the intermittent engine miss! The diagnosis was simple: by connecting a tool called a “vacuum analyzer” to a lab scope and triggering the signal from the #1 cylinder, I noticed a slight variation in the waveform from the #5 cylinder. Although I could lift the valve cover only a few inches due to interference from the air conditioner compressor, I discovered that the #5 exhaust valve guide was completely worn out, which allowed exhaust gases to pass through the guide and overheat the valve spring. The over-heated, carbon-covered spring had weakened to the point of barely closing the exhaust valve. Although the spring would close the valve well enough to a cranking compression test, the weak spring allowed exhaust gas to be drawn into the cylinder on the intake stroke, which diluted the air/fuel mixture and caused the intermittent rough idle condition.

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Scan Tool Help Copyright AA1Car.com A scan tool is a must for automotive diagnostic work today. When your Check Engine Light is on, you have to access the vehicle's onboard diagnostics with a code reader, scan tool or scanner software to find out what's wrong. A scan tool allows you to read faul codes and other diagnostic information.

READING TROUBLE CODES On most 1995 and older pre-OBD2 domestic vehicles, diagnostic trouble codes can be read manually by grounding or jumping certain terminals on the vehicle's diagnostic connector. This puts the powertrain control module (PCM) into a self-diagnostic display mode, causing it flash out the code via the Check Engine Light (Malfunction Indicator Lamp or MIL). You then look up the code number in a reference chart (such as DTC Code Finder) to find out why the light is on.

The problem with reading manual flash codes is that (1) they are no longer used on most 1996 and newer vehicles (one exception is Nissan), and (2) counting the series of flashes can be confusing. Most flash codes use a combination of long and short flashes to indicate double digit codes, and if the vehicle has more than one code, it may be tricky to tell when one code ends and the next one begins. So the preferred method of reading codes on older vehicles is to use a code reader or scan tool.

On 1996 and newer vehicles with OBD2, there are no manual flash codes. You must have a code reader or scan tool to read the codes.

CODE READERS The most basic diagnostic tool is a code reader. A code reader can access and display codes from your vehicle's computer. The least expensive models only display a number while the better ones also provide a definition (some are even bilingual and can display in English, Spanish or French). Code readers typically sell for under $50.

A code reader can also clear codes to turn off the Check Engine light. Some code readers can also display the "ready" status of various OBD II monitors (ready means the monitor has completed its self-check process). But a code reader is NOT a scan tool because it only reads and clears codes. It does NOT display any sensor data or other system operating information. To read sensor and other system data, you need some type of scan tool or scanner software.

An important point to keep in mind here is that a fault code by itself does NOT tell you which part needs to be replaced. The code only tells you that a fault has been detected, not what caused it. The code serves as a starting point for further diagnosis. Many people don't understand this and assume an inexpensive code reader is all they need to "diagnose" and repair their vehicle.

Also, don't assume all code readers display all codes. They all display "generic" or "global" OBD2 codes ("P0" codes).

But some do not display manufacturer "enhanced codes" ("P1" codes), or if they do, the list of codes may be limited to domestic vehicles (Ford, GM & Chrysler) and not include any enhanced codes for Asian or European vehicles.

Something else to check before you buy is the model years the code reader can access. Most code readers are for 1996 and newer OBD2 vehicles with a standard OBD2 16-pin connector. Most code readers cannot read codes on 1995 and older cars or trucks because the connectors are different. However, vehicle-specific code readers are available for older GM, Ford or Chrysler applications. The same is true for BMW, MINI and some other import applications.

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Something else to keep in mind about code readers (and scan tools), is that the list of new DTCs and system data grows with every new model year. Last year's tool may not work on next year's models. Tools get out-of-date VERY quickly, and have to be updated with new software via plug-in memory chips, cartridges or internet downloads from the tool supplier. If you are shopping on ebay for a used code reader or scan tool, make sure it will work on your vehicle, or can be updated to your vehicle.

SCAN TOOLS For advanced diagnostics on today's vehicles, a full feature scan tool is an absolute must. Scan tools for do-it-yourselfers can display sensor values and system data, but DIY scan tools cannot perform various system self-tests such as checking the operation of the fuel pump, cooling fan(s), idle speed control motor or solenoid, EGR solenoid, A/C compressor clutch, fuel injectors, EVAP leak test, EVAP purge controls, etc. This level of diagnostics requires a professional level scan tool (which are EXPENSIVE!) with bidirectional (two-way) communication capability and the proper software for accessing and running these type of tests.

Scan tools have different ranges and capabilities. Entry level "generic" scan tools typically sell for less than $200. They can read and clear codes, display the status of the various OBD II system monitors, and display basic operating data such as loop status (Open or Closed), airflow, coolant temperature, oxygen sensor outputs, throttle position and other sensor readings, and fuel trim values for diagnostic purposes. Most of these tools are fairly versatile and work on all domestic makes (Ford, GM & Chrysler), but may require additional software for Asian and/or European applications.

Entry level scan tools that are sold in auto parts stores are usually designed for do-ityourselfers, and lack bidirectional communications capability for liability reasons.

They may also display only a limited number of "PIDs" (Performance Information Data such as sensor values, switch status and other operational data) compared to a professional level scan tool or factory scan tool.

PROFESSIONAL LEVEL SCAN TOOL FEATURES The more advanced aftermarket professional grade scan tools, by comparison, can do most of the same things an OEM factory scan tool can do. They can access and display all or most of the PIDs (with the proper software), and they can access and run all or most of the OEM self-tests (again, with the proper software).

The better tools typically have better displays, too. These include larger LCD screens with color graphics. The tool may also have multi-channel scope function that allows data to be displayed as a graph or waveform.

This makes is easier to detect certain kinds of problems that may occur too quickly to notice when looking at numerical data. Many scan tools also have a "flight recorder" capability that allows data to be captured while the vehicle is being driven, for later analysis. An add-on 5-gas exhaust gas emission analyzer may also be an option.

Another feature that's available in many professional level scan tools is the ability to flash reprogram PCMs. Flashing a PCM with updated software may be necessary to correct a driveability or emissions issue. Flashing may also be

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necessary if the PCM is replaced. The other option is to get a J2534-compliant "pass-thru" tool that serves as an interface between the vehicle's PCM and a laptop or desktop PC. NOTE: Some claims can be misleading. A vendor may say their product or software package covers a long list of makes and models, but it may be only generic OBD II information. They may not even have enhanced codes for the applications listed. Others may provide all the OBD II codes but no additional codes for ABS, air bags or other systems beyond the engine and powertrain. Some may have limited diagnostics and not include all the factory tests or procedures. If you are not sure exactly what is or is not included, ask before you buy.

Another cost associated with buying a professional scan tool is the cost of annual software updates. Updates are essential for keeping up with changes that occur every year. Update subscriptions can cost up to $800 per year.

If you are looking for info on a particular scan tool, go to the tool supplier's website and browse their product information and/or training videos:

OEM OR AFTERMARKET SCAN TOOL? OEM factory scan tools provide full access to virtually everything, but are very expensive compared to many aftermarket general purpose scan tools (though some of the high end aftermarket tools also cost thousands of dollars depending on their features). An OEM scan tool may cost $5000 up to $12,000 or more!

OEM scan tools include the Tech II for General Motors applications, New Generation Star (NGS) tester for Ford/Lincoln/Mercury, DRB III for Chrysler, and a list of others for the Asian and European makes. Some of these are now obsolete, having been replaced by more advanced PC-based scanner software in dealerships. Even so, for home diagnostic work, you can often find one of these older scan tools reasonably prices on ebay.

Factory scan tools generally provide access to all the diagnostic trouble codes (both "generic OBD II" and "enhanced"), all the on-board self-test procedures, and all of the other on-board electronics beyond engine performance and emissions such as the body control module, ABS module, air bag module, suspension module, climate control module and so on. The OEM scan tool can also be used to "reset" or "initiate" a module if it has been replaced (which is often necessary before the module will function correctly)> Often this involves a special "relearn" procedure that may only be available with the factory scan tool.

The only drawback with OEM scan tools is that most (with some exceptions) are designed to only work on ONE make of vehicle, not all makes and models. Consequently, they are well suited for new car dealer technicians but not general repair shop technicians who usually work on all makes and models.

Most technicians can't afford to own a separate scan tool for each and every vehicle they work on, so most opt for a general purpose scan tool and add software and hardware to expand its capabilities as needed. Some may also buy one or two OEM scan tools if they do a lot of work on a particular make (GM, for example, or an import). And they may also have a basic code reader for making quick code checks.

IS THE SCAN TOOL CAN COMPLIANT? In recent years, the electrical systems on vehicles on late model vehicles have been using a new onboard communications protocol called CAN or Controller Area Network. CAN started phasing in in the early 2000s, and

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became standard on all 2008 and newer cars and light trucks. CAN uses a much higher baud rate to allow faster communication between modules. Because of this, CAN vehicles require a scan tool that is CAN-compliant for diagnostics. Most older scan tools cannot be upgraded to read the newer CAN vehicles. So if you are buying a used older scan tool, keep that in mind.

SCANNER SOFTWARE In addition to dedicated scan tools, you can also buy software that transforms a laptop or desktop PC, PDA, tablet or smart phone into a code reader or scan tool. Some of these offer very basic functions only while others run essentially the same software as an OEM scan tool.

The simplest and cheapest packages that sell for a couple hundred dollars or less essentially give you the ability to plug a laptop, PDA, tablet or smart phone into the diagnostic connector on a 1996 or newer vehicle and use it as a code reader to display and clear generic OBD2 fault codes. The better packages include enhanced codes for specific vehicle applications, and also may include the ability to display various PIDs such as sensor voltages, switch status and so on.

The best software also includes graphics for displaying sensor voltages and other data.

Scanner software for a laptop, PC, tablet or smart phone requires either an interface cable that plugs into the OBD2 connector, or a WiFi or Bluethooth connection so your vehicle can communicate with your electronic device. The scan tool software, by itself, is useless without the cable or wireless interface that connects your computer or electronic device to your vehicle. If you are resourceful and want to save a few bucks, there are numerous sources on the Internet where you can buy interface cables separately, or kits or plans to build your own USB OBD cable.

One of the advantages of using a laptop or desktop PC as a scan tool is having a large display (which makes it easier to read and can display more information on a single page). Most laptops have a screen that measures 12 to 17 inches diagonally, while most PC monitors range in size from 16 to 22 inches or larger. If you have an old PC sitting around gathering dust, you can convert it into a large display color scan tool at a minimal cost (typically $250 to $500 or less for the software, including the interface cable).

Another advantage of using a computer as a scanner is that it can easily be updated by downloading the latest software via the internet. This also can be done with most newer scan tools as well (using a PC as an interface with a USB cable). The updates for DIY scan tools are often free, but for professional scan tools there is usually a fee or yearly subscription to pay.

Dedicated scan tools, by comparison, are designed to be scan tools and nothing else. You cannot surf the Internet with them or check your e-mail or Facebook page. They are for diagnosing cars only. Many professional-grade scan tools have additional hardware circuitry and test leads that allow you to use the same tool as a multimeter or digital oscilloscope to measure voltages, resistance and current. This is an extremely useful feature to have and reduces the need for additional test equipment.

SCAN TOOLS WITH SCOPE DIAGNOSTICS Many high end professional scan tools also have the added ability to function as graphing multimeters or digital storage oscilloscopes.

Being able to display sensor voltages as waveforms makes it much easier to detect problems that are nearly impossible to diagnose any other way.

If you are looking for a multi-purpose tool that can be used as a scanner, multimeter and scope, choose one that can display more than one waveform at a time. Many professional scan tools can simultaneously graph and display up to four different PIDs. When a scope is hooked up to a sensor or circuit, it shows what is

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actually going on inside that device or circuit. Voltage is displayed as a time-based waveform. Once you know how to read waveforms, you can tell good ones from bad ones. You also can compare waveforms against scan tool data to see if the numbers agree (which is a great way to identify internal PCM faults).

A scope also allows you to perform and verify "action-reaction" tests. You can use one channel to monitor the action or input, and a second, third or fourth channel to watch the results. For example, you might want to watch the throttle position sensor, fuel injector waveform, crank sensor signal and ignition pattern when blipping the throttle to catch an intermittent misfire condition.

Using a scope does require a working knowledge of scope basics as well as the limitations of the scope you are using.

Like scan tools, different scopes have different capabilities, so study and compare before you buy.

SCAN TOOL COMPARISON REPORT For an up-to-date report compiled by the National Automotive Service Task Force (NASTF) on which scan tools are required for which vehicle applications, If you would like to read one shop's experience with scan tools and why they own what they own, To find out more about Aftermarket scan tool limitations, and the problems scan tool companies have getting current service information from the vehicle manufacturers,

WHICH SCANTOOL DO TECHNICIANS PREFER? According to a recent (2011) user survey of 400 technicians by iATN (International Automotive Technicians Network), the most popular scan tool form factors are as follows: 61% prefer a hand-held scan tool 28% prefer a laptop with scanner software 11% prefer a tablet with scanner software Those who prefer a traditional hand held scan tool say the units are much faster and easier to use than a laptop or tablet. However, many of the newest professional level scan tools are using Windows-based scanner software in a custom hand held form (Snap-On Modis, Verus, Verdict, etc.). We will probably see more development of Windows scanner software for tablets and custom apps for iPhones and other smart phones as time goes on.

ADVANCED SCAN TOOL DIAGNOSTICS For advanced scope diagnostics, you will want to learn how to access Mode 06 information on a scan tool (most tools that cost upwards of $200 can access Mode 06 today, but you have to know how to find it because it is not clearly marked. Mode 06 data is the raw hexadecimal code data the engine computer looks at when it runs system monitors.

This is useful information to access when a vehicle is experiencing a no-code driveability problem, to verify whether or not a particular sensor or circuit is operating within its specified MIN and MAX values, and to verify a sensor or other component is working properly after it has been replaced.

Information on translating and converting Mode 06 hex code for Ford and GM can be found on the International Automotive Technicians Network website (www.iatn.com). Go to the "Technical Resources" menu, then look in the Ford and Toyota sections. The Mode 06 information is in a downloadable PowerPoint presentation by Paul Baltusis of Ford Motor Company, called "An Introduction to Vehicle Networks, Scan Tools and Multiplexing."

OTHER THINGS YOU WILL NEED IN ADDITION TO A SCAN TOOL 5

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When you buy a scan tool, don't expect to become a diagnostic expert overnight. All scan tools have a learning curve, and it takes some time to figure out what the tool will do (and what it cannot do), which PIDS and other sensor data you should be looking at when troubleshooting different kinds of faults, and what the information means.

Something else to keep in mind is that a scan tool by itself can't fix anything. It takes a brain to operate and use the information provided by the tool. You need to be knowledgeable about OBD2, engine management systems and sensor diagnosis. You also need access to current service information, technical service bulletins and electrical wiring diagrams. If you do not know how a sensor or circuit functions, what causes a code to set, or how a particular sensor or circuit is wired, how are you going to fix the fault?

You also can't rely on codes alone to identify all problems. Many problems never set a code. Some codes can be misleading because of the combination of circumstances that caused them to be set. Other codes may be false codes that never can be eliminated by normal repair procedures. You may have to reflash the computer to fix the problem.

The best advice here is to always check for TSBs, whether you find any codes or not. In many instances, there will be a TSB that covers the problem and will save you hours of frustration.

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SUCCESSFUL

MAF SENSOR Photoillustration by Harold Perry; photos courtesy Wells Manufacturing Corp.

nce in a while we may encounter a total failure of a MAF sensor, one that is, perhaps, short circuited or internally open. Much more common, however, are failure modes in which the MAF sensor has become unreliable, underreporting or overreporting the true airflow into the engine. Indeed, as we shall see, many MAF sensor failures actually result in both underreporting and overreporting!

Before we get down to brass tacks, a brief review of the basics of MAF systems is in order. Fuel control systems for most modern gasoline engines are centered either on MAF or MAP (manifold absolute pressure). MAF systems, which, as their name suggests, measure the weight of incoming air and then meter the appropriate amount of fuel to ensure efficient combustion, are potentially more precise, although MAP systems, which calculate fuel requirements based on engine load, have historically demonstrated greater reliability.

As you already know, combustion is most efficient when the ratio of air to fuel is approximately 14.7:1 by weight.

Mass and weight are essentially synonymous in the presence of a sufficiently strong gravitational field such as the Earth’s. Thus, knowing the weight of the air entering the engine allows the engine controller to meter the exact amount of fuel required to achieve efficient combustion. The controller commands the fuel injectors to open for an amount of time calculated to be sufficient to allow the correct weight of fuel to enter the engine, providing that the fuel’s pressure is known. Fuel delivery is fine-tuned by applying fuel trim corrections derived from the closed-loop feedback of the oxygen sensor(s).

If the entire system is working as designed, fuel trim corrections, expressed as a percentage deviation from the base fuel delivery programming, will be within 10% (either positive or negative) of the programmed quantity. In the absence of a MAF-specific diagnostic trouble code (DTC), what would first lead us to even suspect that a faulty MAF sensor might underlie a particular driveability problem?

To function correctly, all of the air

DIAGNOSIS

BY SAM BELL A broad range of seemingly unrelated or contradictory driveability complaints may arise from MAF sensor performance faults. Use this guide to navigate out of a diagnostic thicket or, better still, to avoid one entirely.

entering an engine’s combustion chambers must be “seen” by the MAF sensor. This means that any vacuum or air leak downstream of the sensor will result in insufficient fuel metering, causing a lean condition in open-loop operation and higher-than-normal fuel trim values in closed-loop. When we encounter a MAF sensor-equipped vehicle exhibiting these symptoms, we need

to check for unmetered airflow first.

Remember, too, that unmetered airflow may not require an external air leak. An incorrectly applied or faulty PCV valve can result in incorrect MAF data where the PCV intake through the breather hose is upstream of the MAF. So, the first two rules of MAF sensor diagnosis are: 1. Find and eliminate all external air

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or vacuum leaks downstream of the MAF sensor. When in doubt, use a smoke machine, or lightly pressurize the intake manifold and spray with a soap & water solution.

2. Verify that the manufacturer-specified PCV valve is correctly installed and functioning as designed. (This is one instance where precautionary replacement may be cost-justified.)

Only after these two steps have been completed can you safely proceed with other diagnostics. The foremost clue that the fault lies with the MAF sensor itself will be excessive fuel trim corrections, usually negative at idle, more or less normal in midrange operation and positive under high load conditions (see “How Contamination Affects Hot-Wire & Hot-Film MAF Sensors” on page 32).

While there are several distinct MAF sensor technologies ranging from hotwire or hot-film to Karman vortex and Corialis sensors, and while MAF sensor outputs may take the form of variable frequency, variable current or a simple analog voltage, the diagnostic principles remain largely the same.

Let’s start with Ford vehicles, for a couple of reasons. First, they are so widespread that most of us are familiar with them. Second, most MAF sensorequipped Ford products make use of a PID (Parameter IDentification) called BARO (barometric pressure). Up to 2001 models, this was an inferred, or calculated, value generated by the PCM (powertrain control module) in response to the maximum MAF flow rates observed on hard wide-open throttle (WOT) acceleration. Where this calculated BARO PID is available, it is of great diagnostic value, since it can confirm MAF sensor accuracy, if only under high flow rate conditions.

To use the BARO PID, you must first know your approximate local barometric pressure. You might consult the BARO PID on a known-good MAP sensor-equipped vehicle. Alternatively, your local airport can provide this data.

Do not rely on local weather stations, however, since these usually report a “corrected” barometric pressure. If weather information is the only available source, a rule of thumb is to subtract about 1 in. of mercury (1 in./Hg) for every 1000 ft. of elevation above sea level. This will yield a rough estimate of your actual local barometric pressure.

For greater accuracy, you can purchase a functional barometer for something less than $40. Compare this data with the BARO PID. A large discrepancy here—say, more than 2 in./Hg—should direct your suspicions toward the MAF. Confirm your hypothesis as follows: First, make sure you have followed the steps outlined in the two rules above.

Next, record all freeze frame data and all DTCs, including pending DTCs. If the OBD monitor readiness status for oxygen sensors shows READY, proceed to the next step. If it doesn’t, refer to the procedures in the following paragraph now. Next, perform a KAM (Keep Alive Memory) reset and drive the vehicle. Make sure your test drive

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Fig. 1 includes at least three sustained WOT accelerations. (It’s not necessary to speed to accomplish a sustained WOT acceleration. Rather than a WOT snap from idle, an uphill downshift at 20 to 30 mph is usually sufficient. The WOT prescription can be met at throttle openings as low as 50% to 70%.) The BARO PID should update from its default reading by the end of the third WOT acceleration. If it’s now close to your local barometric pressure, the MAF sensor is not likely to be faulty. If BARO is not close, try one of the cleaning techniques explained in the sidebar “Keeping It Clean” on page 34, then again reset KAM and take a test drive. If the BARO is still out of range, a replacement MAF sensor is in your customer’s future. Unfortunately, in many 2002 and later Fords, the calculated BARO PID is supplanted by a direct BARO reading

Fig. 3

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Fig. 2 taken from a sensor incorporated into the ESM (EGR System Management) valve, greatly lessening its diagnostic value for our current purposes.

If the oxygen sensor monitor status showed INCOMPLETE above, you’ll have to verify O2 sensor accuracy and performance before performing the KAM reset procedure. Use a 4- or 5-gas analyzer to determine whether the air/fuel ratio is correct in closed-loop operation. The notes about lambda (␭) below should help.

Outside of the Ford family, MAF sensor diagnosis is more difficult. Large fuel trim corrections—either positive or negative—are often the only initial pointer to MAF sensor problems.

Again, any and all air leaks downstream of the MAF sensor must be repaired first. Since accurate fuel trim corrections depend on correct O2 sensor out-

puts, you must verify the functionality of these sensors first. The easiest and fastest way to do this is by checking lambda, a type of measure of the air/fuel ratio. (For a detailed explanation, see my article in the September 2005 issue of MOTOR.) If the O2 sensors are functioning correctly, lambda at idle should be very nearly equal to 1.00 in closedloop. You may wish to check this also at 1500 to 1800 rpm to verify adequate mixture control off idle. Once lambda is found to be correct, the O2 sensors are proven good. Then any fuel trim adjustments must result from unmetered or incorrectly metered airflow or from incorrect fuel delivery.

Distinguishing between fuel delivery problems and MAF sensor problems can be very frustrating. Start by verifying fuel pressure and volume. (Those who rely on pressure alone may regret

Fig. 4

Screen captures: Sam Bell

SUCCESSFUL MAF SENSOR DIAGNOSIS

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SUCCESSFUL MAF SENSOR DIAGNOSIS

Fig. 5 it.) Use your scan tool to record critical data PIDs and graph them for analysis.

Here are a couple of examples: In Fig. 1 on page 30, taken during a period of closed-loop operation, shortterm fuel trims (blue and green traces) for each bank were above 13% at 1100 rpm (red trace), yet dropped sharply negative at 3600 rpm, proving that inadequate fuel delivery was not the problem.

The values indicated in the legend boxes correspond to the readings obtained

Fig. 6 at the indicated cursor position (vertical black line). The vertical white line indicates the trigger point for the recording.

Subsequent diagnostics focused on the MAF sensor and the PCV system.

Take a look at the scan data graph shown in Fig. 2. It shows a car whose faulty fuel pump was unable to deliver sufficient fuel under high load conditions. Notice the very low O2 sensor readings (displayed in blue) corresponding to the cursor (black vertical

How Contamination Affects Hot-Wire & Hot-Film MAF Sensors

H

ot-wire and hot-film MAF sensors calculate airflow based on monitoring the current required to maintain a constant temperature in the sensing element.

When dirt accumulates, the additional surface area allows greater heat dissipation at low airflow rates.

The dirt, however, also functions as an insulator, with an overall net resistance to heat transfer at very high airflow rates.

At idle and under relatively low flow/load rate conditions where the majority of operation may take place, the surface area effect usually predominates, causing a rich condition with fuel trim corrections usually in the range of ⫺10% to ⫺5%. At sustained high flow/load rates, the insulative effect usually takes over, causing a lean mixture needing fuel trim corrections as high as +30%.

Worse still is a complex case of

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“mass confusion” that may arise under hard acceleration when longterm negative fuel trim corrections, learned in closed-loop under lowflow-rate conditions, are applied precisely when positive fuel trim corrections would be more appropriate.

So, for example, when the system goes to open-loop during hard acceleration where the MAF is already underreporting airflow by up to 30%, the PCM may subtract an additional 10% to 15% (LTFT) from the normal fuel delivery calculation, leaving the system as much as 45% leaner than desired!

In midrange operation, the two effects (surface area and insulative properties) may roughly cancel each out, with fuel trims being more or less normal. Additionally, the exact chemistry and configuration of dirt buildups can vary, changing the balance of power between the surface area and insulative effects.

line just to the right of the zero time stamp). Fuel pressure was within spec at idle and at about 2000 rpm, but volume was very low. The sudden dropoff in O2 activity in response to hard acceleration is a characteristic observed in many instances of MAF sensor faults as well.

Ultimately, known-good snapshots, waveforms and other data sets are invaluable. Take a look at the scan snapshot in Fig 3. Does it show good fuel trim and appropriate MAF sensor readings?

Since total fuel trim stays well within the 0 ±10% range throughout the trace, it’s a good bet that the MAF sensor is working well, at least under the sampled conditions.

How about the data set shown in Fig. 4? In fact, the snapshot was taken during open-loop, closed-throttle deceleration when fuel was not being injected, so the O2 sensor PID makes sense. It’s actually a substituted default value inserted whenever the vehicle is in closed-throttle decel mode. What about the reported MAP value? A reading of 4.00 in./Hg shows very high engine vacuum, which jibes with the reported TPS PID. The fuel trim data is within the usually accepted range of 0 ±10%. Good data can come in a variety of formats.

Of course, waveform captures from your scope are often all that are needed to confirm a faulty MAF sensor. In our shop, we’ve found that a snap-throttle MAF test for Ford products should always produce a peak voltage of at least 3.8 volts DC. The snap-throttle test is

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SUCCESSFUL MAF SENSOR DIAGNOSIS performed the same way as for ignition analysis. The idea is not to race the engine, but simply to open the throttle abruptly to allow a momentary surge of maximum airflow as the intake manifold gets suddenly filled with air.

It’s critical that the throttle be opened (and closed) as quickly as possible during this test.

The waveform in Fig. 5 on page 32 is from a known-good MAF sensor. Note the peak voltage of 3.8 volts. The rapid rise and fall after the throttle was first opened is normal and reflects the initial gulp of air hitting the intake manifold walls and suddenly reaching maximum density, greatly reducing subsequent flow. The exact shape of the waveform may vary from model to model, based on intake manifold and air duct (snorkel) design.

What’s the relationship between MAF and engine speed? As Fig. 6 shows, rpm and airflow rate track one another closely under the moderate acceleration conditions during which this screen capture was taken. The similarity of the shapes of the two traces shown

Fig. 7 here suggests, but does not prove, that the MAF sensor is functioning well under these conditions. If the airflow report was consistently increased or decreased by the same factor, say 10% or even 50%, the shape of its graph would remain the same.

Consider the additional plots presented in Fig. 7 above. Does the extra data shed any light on the MAF sensor’s accuracy? Or is this just an example of too much information?

Since short-term and long-term fuel

Keeping It Clean

M

ost MAF sensor failures result from contamination.

Sometimes the dirt is visible, but more often it’s not. Technicians have tried a variety of cleaners, with mixed success. Many use an aerosol brake/electrical parts cleaner, waiting until the MAF sensor is cold. A Ford trainer in my area swears by the most popular consumer glass cleaner. Several top technicians report good results from steam cleaning, while others prefer a spray induction cleaner.

The vast majority of technicians warn that the MAF sensor may be damaged by any type of cleaning where the electrical connector is not held upright. This is particularly true where strong chemicals are used, as they may pool and work their way

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into the delicate electronic circuitry.

To avoid future contamination, be wary of oiled air filters or any that appear likely to shed lint. Poor sealing of air filter housings may contribute to contamination. Never spray an ill-fitting air filter with a silicone lubricant or sealer; such sprays are likely to render the MAF sensor inaccurate. If an engine produces excessive blowby gases, these may contaminate the MAF sensor, as well. Be sure any specified filter breather element is installed. If none is specified, but oil accumulates in the air intake housing, the MAF sensor or associated intake ducts, be sure to investigate and remedy the cause to prevent repeat failures. Be sure to check manufacturers’ TSBs, the iATN archives and other sources as well.

trims remain within single digits throughout, we can be reasonably sure that the MAF sensor is functioning correctly.

Do we really benefit from looking at the O2 sensor data here? We could probably do almost as well without it, since we have both STFT and LTFT, but the O2 trace (blue) serves as an additional crosscheck on the validity of the fuel trim calculations. More importantly, the O 2 sensor trace proves both that an appropriately rich mixture was obtained on hard acceleration and that applied fuel trim corrections were effective throughout the captured data set.

I said at the outset that hard failures were relatively rare, but they do occur from time to time, and I owe it to you to discuss this type of failure as well as intermittent failures. Open-circuited or short-circuited MAF sensors usually set a trouble code, most frequently P0102 or P0103 (low input and high input, respectively). P0100 is a nonspecific MAF sensor circuit fault, while P0104 indicates an intermittent circuit failure.

Checking scan data is a vital first step toward successful diagnosis of any of these codes. On pre-OBD II vehicles especially, unplugging a faulty MAF sensor will often restore a minimum degree of driveability as the PCM reverts to TPS, rpm and/or MAP as fuel determinants. Certain mid-’80s GM vehicles were notorious for intermittent MAF sensor failures. These usually could be easily recreated by lightly tapping with a small screwdriver on the MAF sensor housing at idle. A noticeable stumble occurring with each tap clinches the condemnation (Fig. 8, page 36).

Of course, backprobing the MAF sensor connector for voltage drops at both the power and ground terminals KOER is a required step before any final condemnation. The coincidence of VBATT and MAF both showing 0.0 volts cannot be ignored. Neither should the mouse nest in the MAF, nor the gnawed wires throughout the engine compartment.

Why is this a hard diagnosis? Conta-

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SUCCESSFUL MAF SENSOR DIAGNOSIS minated MAF sensors often overreport airflow at idle (resulting in a rich condition and negative fuel trim corrections) while underreporting airflow under load (resulting in a lean condition and positive fuel trim corrections).

This double whammy makes diagnosis more difficult for a number of reasons: First, many technicians incorrectly eliminate the MAF sensor as a potential culprit because they expect it to show the same bias (either over- or underreporting) throughout its operating range. Second, a lack of a direct MAF fault DTC (such as P0100) is often mistaken to mean that the MAF sensor must be good. Third, the symptoms mimic (among other possibilities) those of a vehicle suffering from low fuel pump output coupled with slightly leaking injectors or an overly active canister purge system. Even sluggish, contaminated or

Fig. 8 biased oxygen sensors may cause similar symptoms. Without appropriate testing, it’s hard to distinguish—just by driving—among certain ignition or knock sensor faults and MAF sensor malfunctions. Additionally, since MAF sensors are somewhat pricey, many technicians are afraid to condemn them, fearing either the customer’s or the boss’ wrath if their diagnosis is not borne out. Perhaps

the biggest obstacle is lack of a comprehensive database of known-good waveforms, voltages and scan data against which to compare the suspect.

My own data set features known-good scan data and scope captures made KOEO, at idle and on snap-throttle. In general, these three data points should be sufficient to identify a faulty MAF sensor even before it sets a fuel trim code.

A bad Bosch hot-wire MAF sensor may be the result of a failed burn-off circuit. Don’t simply replace the sensor; make sure the burn-off is functional. (The purpose of the burn-off is to clean the hot-wire of contaminants after each trip.) Burnoff is usually a key OFF function after engine operation exceeding 2000 rpm.

Burn-off circuit faults may be in the PCM or a relay. The hot-wire should glow visibly red during burn-off.

So what can we conclude from all this? A broad and seemingly unrelated or even contradictory range of fuel system-related driveability complaints may arise from MAF sensor performance faults. Fuel trim data showing excessive corrections from base programming casts strong suspicion on MAF sensor performance issues. After recording all DTCs and freeze frame data, many experienced techs recommend unplugging a suspect MAF sensor to see if basic driveability is improved. Scope traces at idle and on snap-throttle acceleration help verify MAF sensor guilt or innocence.

As usual, a library of known-good scan data and waveforms is invaluable.

The Min/Max voltage feature on your DMM may not be fast enough to catch actual peak voltage on a snap-throttle test, but is usually sufficient for verifying performance of frequency-generating (digital) MAF sensors. If your scope is capable of pulse-width triggering, using that function will provide exact captures of digital MAF sensors in snapthrottle testing.

Visit www.motor.com to download a free copy of this article.

Circle # 27

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SISTEMA DE DIAGNOSTICO OBD II Vicente Blasco

¿Qué es el OBD? Se trata de un sistema de diagnóstico integrado en la gestión del motor, ABS, etc. del vehículo, por lo tanto es un programa instalado en las unidades de mando del motor. Su función es vigilar continuamente los componentes que intervienen en las emisiones de escape. En el momento en que se produce un fallo, el OBD lo detecta, se carga en la memoria y avisa al usuario mediante un testigo luminoso situado en el cuadro de instrumentos denominado (MILMalfunction Indicator Light). El hecho de denominarse EOBD II es debido a que se trata de una adaptación para Europa del sistema implantado en EEUU, además de tratarse de una segunda generación de sistemas de diagnóstico. El OBD, por el hecho de vigilar continuamente las Conector ISO 15031-3 se utiliza con el OBDII y el emisiones contaminantes, ha de tener EOBD . Arriba se muestra el montado en el coche y bajo control no solo a los componentes, abajo el de diagnostico, que se conecta para leer los datos. sino también el correcto desarrollo de las funciones existentes en el sistema de gestión del motor, por lo que se convierte en una excelente herramienta que debe facilitar la diagnosis de averías en los sistemas electrónicos del automóvil.

La incorporación del sistema de diagnosis OBD viene impuesto por las directivas de la Unión Europea que pretenden minimizar y reducir la emisión de determinados gases de los automóviles y evitar la contaminación atmosférica para preservar el medio ambiente y desde . Desde enero de 2000 que entró en vigor la Fase III se obliga al fabricante a incorporar un sistema de vigilancia de la contaminación provocada por el vehículo que informase al usuario de tal situación. Este sistema, encriptado, estandarizado para todos los fabricantes y que convive con el sistema de autodiagnosis propio de la marca, es el EOBD (European On Board Diagnosis)

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Comunicación La comunicación entre la Unidad de Control (ECU) y equipo de diagnosis se establece mediante un protocolo.

Hay tres protocolos básicos, cada uno con variaciones de pequeña importancia en el patrón de la comunicación con la unidad de mando y con el equipo de diagnosis. En general, los productos europeos, muchos asiáticos y Chrysler aplican el protocolo ISO 9141. General Motors utiliza el SAE J1850 VPW (modulación de anchura de pulso variable), y Ford aplica patrones de la comunicación del SAE J1850 PWM (modulación de anchura de pulso)

2 - J1850 (Bus +) 4 - Masa del Vehículo 5 - Masa de la Señal 6 - CAN High (J-2284) 7 - ISO 9141-2 Línea K 10 - J1850 (Bus -) 14 - CAN Low (J-2284) 15 - ISO 9141-2 Línea L 16 - Batería +

Control en los motores de gasolina •

Vigilancia del rendimiento del catalizador

•

Diagnóstico de envejecimiento de sondas lambda

•

Prueba de tensión de sondas lambda

•

Sistema de aire secundario ( si el vehículo lo incorpora)

•

Sistema de recuperación de vapores de combustible (cánister)

•

Prueba de diagnóstico de fugas

•

Sistema de alimentación de combustible

•

Fallos de la combustión - Funcionamiento del sistema de comunicación entre unidades de mando, por ejemplo el Can-Bus

•

Control del sistema de gestión electrónica

•

Sensores y actuadores del sistema electrónico que intervienen en la gestión del motor o están relacionados con las emisiones de escape

Control en los motores diesel •

Fallos de la combustión

•

Regulación del comienzo de la inyección

•

Regulación de la presión de sobrealimentación 2

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•

Recirculación de gases de escape

•

Funcionamiento del sistema de comunicación entre unidades de mando, por ejemplo el Can-Bus

•

Control del sistema de gestión electrónica

•

Sensores y actuadores del sistema electrónico que intervienen en la gestión del motor o están relacionados con las emisiones de escape

Control de la contaminación El estado actual de la técnica no permite, o sería muy caro, realizar la medida directa de los gases CO (monóxido de carbono), HC (hidrocarburos) y NOx (óxidos nítricos), por lo que este control lo realiza la ECU de manera indirecta, detectando los niveles de contaminación a partir del análisis del funcionamiento de los componentes adecuados y del correcto desarrollo de las diversas funciones del equipo de inyección que intervengan en la combustión.

La gestión del motor considera las fluctuaciones como primer indicio de que puede haber un posible fallo, además de para poder efectuar el control de numerosas funciones

Cable con conector de diagnostico OBDII con terminación en conector serie RS232C que permite su conexión aun ordenador o equipo que posea el software de comunicación.

En los vehículos con OBD II se incorpora una segunda sonda lambda que se instala detrás del catalizador para verificar el funcionamiento del mismo y de la sonda lambda anterior al catalizador. En el caso de que está presente envejecimiento o esté defectuosa, no es posible la corrección de la mezcla con precisión, lo que deriva en un aumento de la contaminación y afecta al rendimiento del motor. Para verificar el estado de funcionamiento del sistema de regulación lambda, el OBD II analiza el estado de envejecimiento de la sonda, la tensión que generan y el estado de funcionamiento de los elementos calefactores. El envejecimiento de la sonda se determina en función de la velocidad de reacción de la misma, que es mayor cuanto mas deteriorada se encuentre.

El OBD verifica el correcto funcionamiento del sistema de aire secundario analizando la tensión generada por las sondas lambda, (menor tensión) puesto que la inyección de aire aumenta la cantidad de oxígeno en los gases de escape. La detección por parte de la unidad 3

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de mando de una mezcla muy pobre a partir de la caída de tensión en las sondas presupone el correcto funcionamiento del sistema

¿Qué requerimientos exige el sistema OBD II? El OBD permite estandarizar los códigos de averías para todos los fabricantes y posibilitar el acceso a la información del sistema con equipos de diagnosis universales. Proporciona información sobre las condiciones operativas en las que se detectó y define el momento y la forma en que se debe visualizar un fallo relacionado con los gases de escape.

Los modos de prueba de diagnóstico OBDII han sido creados de forma que sean comunes a todos los vehículos de distintos fabricantes. De esta forma es indistinto tanto el vehículo que se esté chequeando como el equipo de diagnosis que se emplee, las pruebas se realizarán siempre de la misma forma.

Modos de medición El conector de diagnosis normalizado, deber ser accesible y situarse en la zona del conductor. Los modos de medición son comunes todos los vehículos y permiten desde registrar datos para su verificación, extraer códigos de averías, borrarlos y realizar pruebas dinámicas de actuadores. El software del equipo de diagnosis se encargará de presentar los datos y facilitar la comunicación. Los modos en que se presentan la información se halla estandarizado y son siguientes: •

Modo 1 Identificación de Parámetro (PID), es el acceso a datos en vivo de valores analógicos o digitales de salidas y entradas a la ECU. Este modo es también llamado flujo de datos. Aquí es posible ver, por ejemplo, la temperatura de motor o el voltaje generado por una sonda lambda

•

Modo 2 Acceso a Cuadro de Datos Congelados. Esta es una función muy útil del OBD-II porque la ECU toma una muestra de todos los valores relacionados con las emisiones, en el momento exacto de ocurrir un fallo. De esta manera, al recuperar estos datos, se pueden conocer las condiciones exactas en las que ocurrió dicho fallo. Solo existe un cuadro de datos que corresponde al primer fallo detectado

•

Modo 3 Este modo permite extraer de la memoria de la ECU todos los códigos de fallo (DTC - Data Trouble Dode) almacenados

•

Modo 4 Con este modo se pueden borrar todos los códigos almacenados en la PCM, incluyendo los DTCs y el cuadro de datos grabados

•

Modo 5 Este modo devuelve los resultados de las pruebas realizadas a los sensores de oxigeno para determinar el funcionamiento de los mismos y la eficiencia del convertidor catalítico

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Modo 6 Este modo permite obtener los resultados de todas las pruebas de abordo

•

Modo 7 Este modo permite leer de la memoria de la ECU todos los DTCs pendientes

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•

Modo 8 Este modo permite realizar la prueba de actuadores. Con esta función, el mecánico puede activar y desactivar actuadores como bombas de combustible, válvula de ralentí, etc

Detección de a averías en el cuadro de instrumentos En el cuadro de instrumentos se dispone de un testigo luminoso de color amarillo con el ideograma de un motor. Este testigo se enciende al accionar la llave de contacto y debe lucir hasta unos 2 segundos después del arranque del motor. Esta es la forma en que se verifica el correcto funcionamiento del testigo, por parte del técnico o del usuario.

•

Destellos ocasionales indican averías de tipo esporádico.

•

Cuando el testigo permanece encendido constantemente existe una avería de naturaleza seria que puede afectar a la emisión de gases o a la seguridad del vehículo.

•

En el supuesto que se detecte una avería muy grave susceptible de dañar el motor o afectar a la seguridad, el testigo de averías luce de manera intermitente. En este caso se deberá parar el motor

Visualización en un ordenador con software de comunicación mostrando los datos de averías registradas por el sistema OBD.

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Códigos de averías El formato de los códigos de averías presenta una codificación común a todos los sistemas con cinco dígitos:

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Scan Tool Basics This will help you prepare for the NC3 – Snap‐on Scan Tool Certification .

Front‐Door vs Back‐Door Diagnostics To diagnose a computer control system you can go to the “Front Door” or the “Back Door”. The Front Door is where sensor data (input) enters and actuator data (output) leaves the computer. You go in the Back Door by using a scan tool to find what the computer is thinking.

Diagnosis often starts at the Back Door. The back door is found at the data link connector (DLC) where you connect the scan tool to the vehicle. On a modern vehicle you can use a scan tool to access the Back Door for multiple vehicle control modules such as the engine, transmission, instrument cluster, tire pressure monitor, ABS system, power windows, etc. Back Door Checks include: Diagnostic Trouble Codes (DTC’s), Input and Output Data (called Parameter Identifiers or PID’s), Graphing PID Data (used to view the relationships between different PID’s), and using the diagnostic Troubleshooter. The Troubleshooter software found in the scan tool will list procedures to test that component or system.

The scan tool (back door) will help you decide which Front Door tests are needed to solve the problem. Front Door tests can be made on input signals (from sensors to the computer), or output command signals used to control the various actuators (like fuel injection, ignition timing, etc.) just remember, The Front Door is what is actually happening outside of the computer and the Back Door is what the computer “thinks” is happening.

Scan tool data (input – output data) and Diagnostic Trouble Codes (DTC’s) are all found at the back door. Once you know which system to check, you diagnose that system using Front Door diagnostic tests.

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The scan tool is a BACK‐DOOR directional tool. It never tells you the cause of a problem, only what’s being affected and where to look. The cause for the malfunction will almost always be found through the FRONT DOOR. Who needs to use a scan tool?

It the past only driveability or engine performance technicians needed to use a scan tool. On modern vehicles you will often use a scan tool to bleed the brakes, perform and alignment, repair a power window, change the tires, or even change the oil.

How do I connect the scan tool?

Here is a picture showing the controls of the Solus Pro which is the primary scan tool we will be using in this class.

Power ON the scan tool, then identify the vehicle you are working on using the Thumb Pad and the Y or N buttons. It is easy to use these scan tool control buttons once you have tried it a few times.

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Here is what you see when you first turn on the Solus Pro

As you progress through the menu, it will instruct you to use a specific key such as the K‐20 key or the S44 key. Below is a picture of what those keys look like.

These plug in to the long black communication cable for the Solus Pro. The next step is to find the Data Link Connector (DLC) inside your vehicle.

The DLC is a 16‐pin connector found on OBDII equipped vehicles. OBD‐II standards specify the DLC be located under the dash near the steering column.

If you can’t find it, the Solus Pro will tell you where the DLC is.

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Once you have identified the vehicle on the scan tool, used the proper key, and connected the communication cable to the DLC, you will need to turn the ignition key to RUN. The Solus Pro can now “talk” to the vehicle control modules.

What can a scan tool do?

Your scan tool can access many vehicle control modules.

The Powertrain Control Modules (PCM) will control your engine and transmission. Modern vehicles have many more control modules. There will be a control module for the instrument cluster, another module for the anti‐lock brakes, one for the air bags and often there is an electronic control module in each of the doors. Some vehicles have over 30 different control modules.

It is important to access these control modules to perform tasks such as setting tire pressure monitors, re‐initializing body controls like power windows, bleeding brakes, diagnosing dash gauges, etc.

Your scan tool will display Diagnostic Trouble Codes (DTC’s).

Diagnostic Trouble Codes are set when the computer decides a system is not working correctly. The computer will set a code and may illuminate the Malfunction Indicator Lamp (MIL) to alert the driver. Diagnostic Trouble Codes only direct you to which system needs diagnosis, they will not tell you what to replace! For help in diagnosing DTC’s Snap‐on scan tools provide the Fast‐Track Troubleshooter. This is a large database of diagnostic procedures that can help you quickly find the root cause of the Diagnostic Trouble Code.

Your scan tool will show all the Parameter Identifiers (PID’s) PID’s are the name we use to represent all the input (sensor) and output (actuator) data. Input Data comes from vehicle sensors and Output Data is commands sent to the vehicle actuators. PID data is the “Back Door” of your computer system and shows what the control module thinks is happening. For instance the PCM monitors the Engine Coolant Temperature. The PID for engine temperature is ECT. When it is cold the PCM decides to add more fuel by keeping the fuel injectors on longer. The input signal is from the ECT which is a sensor.

To add more fuel an output signal goes to the fuel injectors, which are actuators.

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PID data will be numbers (like 755 RPM or TPS (throttle position) of 93%. Some scan tools will display only those numbers (Text). With the Solus Pro you can view PID data three different ways. You can view the data as Text, a PID List, or a Graph. By graphing PID data you can view the relationship between any sensor and actuator. It will show how the PID data changes over time.

Here we are viewing the relationship between the TPS (Throttle Position Sensor) and engine RPM. The RPM should go higher when we open the throttle and lower as we close the throttle. At the left end of the graph we see the throttle is held steady about half way open and the RPM is going Up. When the throttle is allowed to close the RPM goes down. This is all normal operation. Then the TPS drops to zero, but the RPM goes back up. Opening the throttle is what causes engine RPM to increase, however the PID data shows the TPS as fully closed. This relationship of closed throttle while RPM goes UP indicates there is a defect in the TPS sensor or the wires going to the TPS.

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Your scan tool can run Functional Tests that fall into four categories.

1) Information tests, 2) Toggle tests, 3) Variable Control tests, and 4) Reset tests.

Information tests provide information such as the VIN number and the Calibration Part Number. This information is useful when checking to see if the computer has been updated, or when installing a replacement control module.

Toggle tests allow you to ask the control module to turn ON or OFF various actuators. An example would be to request that the Malfunction Indicator Lamp be turned ON or OFF. This is an easy way to test the MIL bulb to see if it is blown out. Another test might be to toggle ON/OFF the fuel injectors one at a time to see if the engine RPM drops the same amount for each cylinder. Toggle tests are found under Functional Tests >> Output Controls.

Variable Control tests are also found in Functional Tests >> Output Controls.

A variable test can command an actuator to run through it’s full range of adjustment. For example the customer is complaining that the fuel gauge will not go past ½ full. By selecting Functional Tests >> Output Controls >> Variable Control >> Fuel Gauge Enable (%) you can command the fuel gauge to display from 0% (empty) to 50% (1/2 full) to 100% (full). If the gauge now reads full, the problem is most likely in the fuel sending unit. If the variable control test cannot get the gauge to read past ½ full, the dash gauge must be defective.

Reset tests are necessary when installing certain components. For example on some engines replacing the crank position sensor (CKP) will require the computer to “re‐learn” the new CKP sensor signal. This reset test is called CKP Variation Learn. On these engines, if you replace the sensor without performing the reset test, the engine may not idle at the correct speed.

When should I use the scan tool?

When you are diagnosing any engine performance issue the scan tool should be one of the first diagnostic steps. By looking for codes or viewing PID data you find which direction your diagnostic path should take. When diagnosing it is a good idea to check for Technical Service Bulletins (TSB’s). SnapOn scan tools will provide troubleshooter software that uses this TSB information to help with your diagnosis. While a scan tool will seldom, if ever, isolate the cause of a problem, it will send you in the right direction and guide you as to what to check next.

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The MIL lamp is ON but there are no codes!

Upon occasion you will have a vehicle with the Malfunction Indicator Lamp illuminated but your scan tool does not display any code. All this means is that you have not looked in the proper control room. Powertrain Control Modules on modern vehicles all have two basic “Control Rooms”. They are the Original Equipment Manufacturer (OEM) room and the On Board Diagnostic (OBD‐II) room.

OEM software uses communication standards set by the specific vehicle manufacturer. There are many different standards used and they change depending upon model and year. This is why you need the proper Key hooked into the Modis Pro communication cable!

OBD‐II software uses a communication standard set by the Environmental Protection Agency. All manufacturers must use the same communication standard for OBD‐II functions.

The OBD‐II room is in charge of the MIL. It is the OBD‐II control room that will decide when to turn on or off the Malfunction Indicator Lamp. It also captures and stores PID data present at the time the MIL was turned ON. This is called Freeze Frame data and can be very useful in deciding what was happening when the failure occurred.

An experienced technician will check both the OEM room and the OBD‐II room when diagnosing the vehicle.

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The only way to learn a scan tool is to practice with it!

The more you use it, the more powerful of a diagnostic tool it will become. As a beginner you will not know what many of the PID data abbreviations stand for.

Even experienced technicians will not know them all. When you find a PID you do not understand, go to: Troubleshooter >> Fast Track Data Scan (Normal Values).

Here the Solus Pro will tell you what that PID means and provide normal or typical data values for that PID. Do not hesitate to explore the many features of the Troubleshooter.

Which scan tool should I purchase?

The very cheapest scan tools are often called code readers. They will only give OBD‐II generic codes. There are many Diagnostic Trouble Codes (DTC’s) stored in the OEM room of the PCM that will not show up on a code reader. Also code readers will not display PID data which is vital to diagnosing a modern vehicle.

Because all OBD‐II control rooms use a standardized communication protocol some less expensive scan tools will only talk to the OBDII control room. They will show DTC’s and PID data available in the OBD control room only. Remember how the OBDII room turns on the MIL? Just because the MIL lamp is OFF does not mean there are no codes. The OEM room will store codes and PID data not found in the OBD room. A professional needs a scan tool that talks to both the OBDII room and the OEM room found in modern vehicles.

A quality scan tool with all the features you need to diagnose modern vehicles is not cheap, and they get more sophisticated every year. For this reason I always caution students to wait on buying a scan tool. You won’t make much money when you first start, and the shop you work for should have one or more scan tools to help you with the tasks an entry level‐apprentice technician performs.

It takes time and effort to gain experience and competence. If you work hard and keep studying you soon will be earning more money to help buy this expensive tool. Also, by the time you really need to purchase your own scan tool they will be faster, better, and maybe even cheaper.

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DOING IT ALL WITH

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Photoillustration: Harold A. Perry; images: Thinkstock, David Kimble, Sun & General Motors

T

he Greek root gen- under lies many words in common parlance—generic is one of them.

Your medical insurance provider and your pharmacist both know that when it comes to prescriptions, generic equivalents can save us all big money, with identical results. In the last few years, generic has, for complex reasons, become a pejorative term, often used to convey the idea of something of lesser quality than a socalled name-brand alternative.

Yet, for diagnostic purposes, the generic datastream sometimes offers a better window into powertrain management operating conditions than even the name-brand “enhanced” or “manufacturer-specific” interface can. In fact, even though I own several much more powerful and expensive scan tools, I routinely use the generic interface residing on the cheapest of the bunch as my go-to choice for initial code retrieval and data analysis.

This particular machine, an aging AutoXray EZ6000, offers no bidirectional controls above code clearing, but has the signal virtues of speed and a very high overall connectivity rate. It also quickly compiles a printable report which includes current operating PIDs, DTCs (including pending codes) and freeze frame data, all of which are obviously useful. Individual monitor completion status requires a separate query, as do both Mode $05 (oxygen sensor test results) and Mode $06 (monitor self-test results) data. Its nice graphing program makes data analysis easy after a road test, and I’m actually happy that you cannot both read and record data simultaneously, as the trees in my neighborhood view that particular behavioral combination as an excuse to jump out in front of you.

One of the primary benefits of the

BY SAM BELL A resourceful diagnostician knows complicated and expensive equipment isn’t always needed. Tools with a narrower focus, combined with an enlightened approach, allow him to get the job done.

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GENERIC DATASTREAM generic datastream stems from the requirement that it not display substituted values. While many so-called enhanced interfaces offer access to a greater number of data PIDs, some of these may reflect substituted values not based on current operating data. For example, most Chrysler products will substitute a reasonable guess for the actual intake manifold vacuum value when the MAP sensor is unplugged. If you look in the enhanced datastream, you’ll see that value varying quite believably as you rev the engine or drive the vehicle. If you look at MAP_Volts, however, you’ll see a fixed value reflecting reference voltage (Vref) for the sensor circuit. But how often do you actually look at that PID instead of the vacuum reading?

While substituted values are prohibited in the generic datastream, calculated values are not. Thus, for example, an ECT PID of ⫺40°F reflects the calculated temperature of an open ECT sensor circuit. In such cases, Toyota, for example, has for many years, then substituted a value of 176°F in its enhanced datastream, but not in the generic data.

In our unplugged Chrysler MAP sensor example above, using a generic interface, you’d see an unmoving value of something in the neighborhood of 255kPa or higher, corresponding to a boost pressure of about 25 psi above atmospheric.

As a technical consultant to our state EPA, several times a year I encounter vehicles which have failed our OBD II plug & play state emissions test for a MIL-on condition with one or more current DTCs that simply do not appear in the “enhanced” interface, but which are readily retrieved using a generic hookup. I’m afraid I can’t shed a lot of light on why this would occur since, clearly, it should not. Thus far, I have not encountered this issue in any 2008 or later vehicles. There seem to be a few makes

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which are more prone to this problem, but my data set is too sparse to be certain of any meaningful correlation. For the moment, suffice it to say that the state’s testing interface is also a generic one, and, apparently, there are instances in which a DTC may set but not be retrieved via even the factory scan tool. On these occasions, only a generic interface will work. As the saying has it, truth is stranger than fiction.

An additional advantage of using the generic datastream becomes apparent when you’re working on a vehicle for which your scan tool doesn’t provide an enhanced interface. Don’t laugh; I’ve had students call me up to ask what to do because they didn’t have a scan tool that offered, say, a Saab or Daihatsu option. A gentle reminder that they could at least start in the generic interface usually nets an embarrassed oops! Because the generic interface contains the data most critical to engine operations (see the starred items in the “Generic PIDs” list on page 24), it’s normally sufficient to rule in or rule out a particular area of concern such as fuel delivery, for example, early in the diagnostic process.

While you might well prefer to work with a dealer-equivalent scan tool in almost all cases, in the real world you may not be able to justify buying a tool with limited utility vis-à-vis your regular customer base.

Let’s take a look at what the generic interface typically offers these days (see the screen captures on this page). The J1979 SAE standard specifically defines 128 generic data PIDs, but not all manufacturers use or support all of them.

Some, such as Mode $01, PID$6F (current turbocharger compressor inlet pressure), are highly specialized and won’t apply to most current-production vehicles, while others, such as PID $06 (engine RPM), are pretty universal. A typical PID list of current values (Mode $01) or of freeze frame values (Mode $02) would include some or all of the 74 items listed in the generic PIDs list.

Your scan tool may use slightly different acronyms or abbreviations to identify various data items.

Most of the PIDs in the list are probably familiar to you, but a few may have you scratching your head. As you see,

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Screen captures: Sam Bell

DOING IT ALL WITH GENERIC DATASTREAM

These two screen shots show the 60 lines of generic data available from a known-good 2014 Mazda CX-5, as captured via a Snap-on SOLUS Ultra scan tool.

starting with a model year 2005 phasein, several new parameters have been added to the original generic data list.

These include both commanded and actual fuel-rail pressure, EGR command and EGR error calculation, commanded purge percentage, commanded equivalence ratio and a host of others, including many diesel-specific PIDs. In-use counters may also indicate how many times each of the various onboard monitors has run to completion since the codes were last cleared. The list on page 24 includes most of the generic PIDs currently in widespread use. However, since not all manufacturers support all PIDs, and since their choices may vary by model, engine and/or equipment, the list given here represents only a portion of the PIDs

potentially supported. Additionally, manufacturers are free to establish and define supplemental modes and PIDs which may or may not be accessible via a generic interface. All ECUs with authority or control over emissions-related issues, however, must be accessible via the generic interface.

From our generic PIDs list, I want to focus on commanded equivalence ratios first. In essence, this is the PCM’s way of reporting how rich or lean a mixture it’s commanding. The PID is presented in a lambda format, with 1.0 indicating a stoichiometric (ideal) air/fuel ratio.

Larger numbers indicate more air—a command to run at a leaner air/fuel ratio—while numbers less than 1.0 indicate a correspondingly richer mixture.

If you have a gas analyzer capable of

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DOING IT ALL WITH GENERIC DATASTREAM displaying lambda, it should coincide extremely well with the Commanded Equivalence PID. As with all fuel trim-related issues, it’s

T

he five starred (★) critical PIDs in the list below are the most influential inputs. Virtually all the others function merely to fine-tune (trim) the basic spark and fuel (base map) commands mapped out in response to these PIDs. The cause of any fuel trim corrections (STFT, LTFT) beyond the range of approximately ⫾5% must be investigated.

Standards Compliance - such as OBD II (Federal), OBD II (CARB), EOBD (Europe), etc.

MIL - malfunction indicator lamp status (off/on) MON_STAT - monitor completion status since codes cleared DTC_CNT - number of confirmed emissions-related DTCs available for display ★RPM - revolutions per minute: also, engine crankshaft (or eccentric shaft) speed, sourced from the CKP ★IAT - intake air temperature ★ECT - engine coolant temperature ★MAP and/or ★MAF - manifold absolute pressure or mass airflow, respectively ★TPS or ★TP - throttle position sensor, usually given as calculated percentage; see absolute TPS below CALC_LOAD - calculated, based on current airflow, as percentage of peak airflow at sea level at current rpm, with correction for current BARO LOOP - status: closed, closed with fault, open due to insufficient temperature, open due to high load or decel fuel cut, open due to system fault STFT_x (per bank) - shortterm fuel trim; the percentage of fuel added to or subtracted from the base fuel schedule (for speed, load, temperature, etc.) in order to achieve stoichiometry as determined by the relevant air/fuel or O2 sensor

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best to check this PID at idle, at about 1200 rpm and at about 2500 rpm. If your actual tailpipe measurements don’t coincide with the PID, be sure to check

for any exhaust leaks first. If there are none, you’ll have to check for factors that could account for the discrepancy, such as fuel pressure faults, vacuum

Generic PIDs LTFT_x (per bank) - long-term fuel trim VSS - vehicle speed sensor HO2SBxSy - heated oxygen sensor, Bank x, Sensor y, such as B1S2 for a bank 1 downstream sensor IGN_ADV - ignition timing, measured in crankshaft degrees SAS or SEC_AIR - commanded secondary air status off/on; may include information such as atmosphere, upstream or downstream of converter, commanded on for diagnostic purposes RUN_TIME - seconds since last engine start; some manufacturers stop the count at 255 seconds DISTANCE TRAVELED WITH MIL ON – in miles or km FRP - fuel rail pressure relative to intake manifold pressure FRP_G - fuel rail pressure, gauge reading O2Sx_WR_lambda(x) - wide range air/fuel sensor, bank x, equivalence ratio (0-1.999) or voltage (0-7.999) EGR - commanded EGR percentage EGR_ERR - deviation of sensed or calculated position from commanded position, percent PURGE - commanded percentage FUEL_LVL - fuel level input percentage; can provide especially invaluable information in freeze frame diagnostics of misfire codes set under “ran-out-ofgas” conditions; unfortunately, not universally implemented WARMUPS - number of warmups since codes cleared; a warm-up is an ECT increase of at least 40°F in which the ECT reaches at least 160°F DIST SINCE CLR - distance since codes cleared EVAP_PRESS - evaporative system pressure

BARO - absolute atmospheric pressure (varies with altitude and weather) O2Sx_WR_lambda(x) - equivalence ratio or current - wide range air/fuel sensor , position x, equivalence ratio (0-1.999) or current (-128mA to +127.99mA) CAT_TEMP BxSy - catalyst temperature by bank and position (may be wildly unreliable) MON_STAT - monitor status, current trip CONT_MOD_V - control module voltage; usually measured on the B+ input for the KeepAlive-Memory (KAM) but may be measured on a switched ignition input line ABS_LOAD - absolute load, percentage, 0-25,700% REL_TPS - relative throttle position percentage AMB_AT or AMB_TEMP - ambient air temperature; where used, usually measured in front of the radiator, while IAT or MAT (manifold air temperature) are usually collected in the intake ductwork, or inside the throttle body or intake manifold, respectively ABS_TPx - absolute throttle position, percentage, sensor B or C APP_x - accelerator pedal position sensors D-F TP_CMD - commanded throttle actuator percentage MIL_TIM - time run with MIL on, minutes FUEL_TYP - fuel type ETOH_PCT or ETH_PCT ethanol fuel % ABS_EVAP - absolute evap system vapor pressure, 0327.675kPa EVAP_P or EVAP_PRESS - evap system vapor pressure (gauge), from -32,767 to +32,768Pa STFTHO2BxS2 – short-term secondary (postcatalyst) oxygen sensor trim by bank

LTFTHO2BxS2 - long-term secondary oxygen sensor trim by bank HY_BATT_PCT - hybrid battery pack remaining life, percentage E_OIL_T or ENG_OIL_TEMP engine oil temperature INJ_TIM - fuel injection timing, in crankshaft degrees from ⫺210° BTDC to ⫹302° ATDC FUEL_RAT - engine fuel rate in volume per unit time—e.g., liters per hour, gallons per minute, etc.

TRQ_DEM - driver’s demand engine, percent torque TRQ_PCT - actual engine, percent torque REF_TRQ - engine reference torque in Nm (0 to 65,535) TRQ_A-E - engine percent torque data at A=idle; B, C, D, E = defined points AFC - commanded diesel intake airflow control and relative intake airflow position EGR_TEMP - exhaust gas recirculation temperature COMP_IN_PRESS - turbocharger compressor inlet pressure BOOST - boost pressure control VGT – variable-geometry turbo control WAST_GAT - wastegate control EXH_PRESS - exhaust pressure TURB_RPM - turbocharger rpm TURB_TEMP - turbocharger temperature CACT - charge air cooler temperature EGTx - exhaust gas temperature, by bank DPF - diesel particulate filter DPF_T - diesel particulate filter temperature NOX - NOX sensor MAN_TEMP - manifold surface temperature NOX_RGNT - NOX reagent system PMS - particulate matter sensor

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DOING IT ALL WITH GENERIC DATASTREAM leaks or a biased oxygen or air/fuel sensor. If you observe a close correlation with lambda, you’ll be able to use this PID with confidence in lieu of actual lambda readings while conducting additional tests.

In general, you should expect this PID to read very close to 1.00 at idle in closed-loop operation with conventional oxygen sensors in the upstream positions. (Wide-range air/fuel [WRAF] ratio sensors may target alternate values under various driving conditions, typically targeting a leaner mix under lightthrottle cruise, for example. Additionally, vehicles using gasoline direct injection [GDI] may deviate from stoichiometry even at idle or under light-throttle cruise conditions.) Keep in mind that the name says a lot: This PID reports the command, not necessarily the effect of the command.

Once in a blue moon you may find that commanded equivalence ratio seems to travel exactly opposite from lambda, so that a Com_Eq_Rat of .95 corresponds to an actual lambda value of 1.05, for instance. After the one instance in which I’ve encountered this, I eventually learned to think of the PID value as a deviation from 1.00, then move exactly that far in the opposite direction. (An unfortunate computer crash led to the OBD - on-board diagnostics.

OBD II - second-generation OBD, as specified by SAE J1979.

EOBD - Euro-specification OBD; slightly different from SAE-spec.

JOBD - Japanese-specification OBD; slightly different from SAE-spec.

DTC - diagnostic trouble code; Pcodes refer to powertrain management faults; U-codes flag communication network errors; B-codes relate to faults in body system management; C-codes are chassis system based.

PDTC - Permanent DTC; one that cannot be cleared directly via scan tool command; such codes will selfclear after the affected monitors have successfully run to completion with no further faults. PDTCs are written into a section of nonvolatile memory, so they persist even if the

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Fuel Type Table: Mode $01, PID $51 Value Description 0 .........Not available 1 .........Gasoline 2 .........Methanol 3 .........Ethanol 4 .........Diesel 5...........LPG (liquid propane gas) 6...........CNG (compressed natural gas) 7 .........Propane 8 .........Electric 9..........Bifuel running gasoline 10..........Bifuel running methanol 11 ........Bifuel running ethanol 12 ........Bifuel running LPG 13 ........Bifuel running CNG 14.........Bifuel running propane 15 .........Bifuel running electricity 16.........Bifuel running electric and combustion engine 17 ........Hybrid gasoline 18 ........Hybrid ethanol 19 ........Hybrid diesel 20 ........Hybrid electric 21.........Hybrid running electric and combustion engine 22 ........Hybrid regenerative 23 ........Bifuel running diesel Any other value is reserved by ISO/SAE. There are currently no definitions for flexible-fuel vehicles.

Glossary battery is disconnected and all capacitors are discharged.

PID - parameter identification; a value found in current or freeze frame data; may indicate a sensor reading, calculated value or command status.

In a nongeneric (enhanced) interface, may indicate a substituted value. $- or -$ - prefix or suffix indicating that an alphanumeric string is hexadecimal (presented in base 16.) The J1979 specifications which establish the OBD II protocol are written using hexadecimal notation throughout.

Datastream - a set of PID values, DTCs, test results and/or PDTCs; the display of such data on or via a scan tool.

Freeze frame - a set of PID values indicating then-current data written into the PCM’s memory when a DTC

loss of my notes from that vehicle, and I can no longer remember even which foreign nameplate make it was, much less the year, model and engine. What I do remember is that it sure threw me for a loop! I also remember rechecking this at the time with another scan tool with the same result, so I suspect that it was simply the result of a mistranslation somewhere along the way, and not a tool glitch per se.)

One more note on the commanded equivalence ratios PID: You’ll find it in use for diesels as well. Stoichiometric conditions for gasoline engines result in an air/fuel ratio of approximately 14.7:1.

The advent of oxygenated fuels has accustomed us to seeing lambda values showing slightly lean, up to as high as 1.04 in some cases, with no apparent fault. Since fuel blends vary both regionally and seasonally, normal values for your area may differ. With diesels, the ratio is closer to 14.5:1, with propane running best at 15.7:1 and natural gas working out to about 17.2:1. If you’re using your gas analyzer on a vehicle burning one of these fuels, you’ll have to reset your lambda calculations accordingly.

Most gas analyzers with a computer plotting interface readily accommodate multiple fuel types, usually from the setup menu. In the case of flex-fuel sets, similar to an aircraft flight recorder. Note: Freeze frame data is erased when codes are cleared; be sure to read and record before clearing DTCs. CAN - controller area network; also, communication via the same.

Monitor - one or more self-tests executed by the OBD system to determine whether a specific subsystem is functioning within normal limits.

Monitor status changes to incomplete or “not done” when DTCs are cleared, and returns to complete or “done” once all relevant self-tests have been run. A monitor status showing completion is not a guarantee of a successful repair unless there are no codes and no pending codes, and unless the vehicle has been operated under conditions similar to those under which a previous fault had occurred (see freeze frame).

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DOING IT ALL WITH GENERIC DATASTREAM cars, check the ETOH_PCT PID to help your analyzer figure out the correct stoichiometric ratio. Once you’ve made the proper selection, you can work from lambda without bothering to know or remember the exact stoichiometric ratio involved.

I was certainly glad to see the appear-

ance of purge data in the generic list, as knowing the commanded purge status can assist in diagnosing several types of driveability faults above and beyond evap leaks and malfunctions. Remember, however, that this PID reflects only the current commanded state, not necessarily what’s actually happening.

The PIDs for EGR Command and EGR Error are likewise helpful. Depending on the interface you use, however, EGR_Error may be reported “backwards,” with 100% indicating that command and position are in complete agreement and 0% indicating that one shows wide-open while the other shows shut. (I’ve seen this on numerous Hondas, where a 99.5% “error” actually meant that the valve was closed as commanded.) As usual, a few minutes checking known-good vehicles can help avoid many wasted hours hunting problems that aren’t really there.

Other new PIDs inform us of the mileage since the last time the codes were cleared as well as the distance driven since the MIL first illuminated for any current codes. Both of these pieces of information can be useful, especially if yours is not the first shop to look at a particular problem. In the case of intermittent faults, they can also help give you a better idea of just how frequently the issue does arise.

Beyond PIDS

Circle #16

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Potentially both more helpful and more problematic are the new Permanent DTCs found in mode $0A. These cannot be cleared directly via a scan tool, but will be self-erased once the corresponding monitors have successfully run to completion. Attempts to circumvent plug & play emissions tests by simply clearing codes without fixing the underlying causes led to the development of these Permanent DTCs. While there are times when I would rather just “kill the MIL,” the PDTCs make me take the extra time to more fully educate my customers and to verify the efficacy of my repairs, often by resorting to Mode $06 data analysis.

The key thing to remember when working with Mode $06 data is that it’s entirely up to the OEM to define all TID$, CID$, MID$, etc. These definitions can vary by year, engine, model and/or equipment even within the same OEM division, so be sure to verify the accuracy of any information you’re using to interpret this data before you get yourself in trouble. Also remember that many manufacturers

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populate their Mode $06 datastream with “placeholder” values after codes are cleared and until affected monitors have run to completion. This is a strong argument for waiting as long as possible before clearing codes.

Probably 90% of the MIL-on complaints we see in my shop are resolved using “just” a generic scanner, coupled, of course, with a few decades of experience! Nevertheless, since a generic scan interface can take you only so far, there are certainly other times when we break out one of our more sophisticated scan tools with bidirectional functionality, access to additional PIDs, guided diagnostics, etc.

Especially in an older vehicle, the generic communications data rate (baud speed) may also seem slow by today’s standards. After an initial scan, this limitation can often be overcome by selecting a relatively small number of PIDs relevant to the problem at hand.

All vehicles since 2008 support CAN communications even in the generic interface. The effective data transfer rates

here are plenty quick enough for almost any practical purpose.

Since OBD II generic standards do not apply beyond P-codes (and some Ucodes), any full-service shop needs one or more scanners to deal with B-, Cand most U-code issues. Remember, though, that many OEMs illuminate TRAC, VSC and/or ABS lights in response to any P-code. This is nearly universally true in the case of drive-by-wire (electronic throttle body) applications, but may be found in many other instances as well. In all such cases, you must resolve the P-code issue first, before worrying about any of these sideeffects codes. If you have an appropriate interface, once you’ve killed the MIL, clear those extra codes as well, so the next tech doesn’t find them still in memory if and when a legitimate B- or C-code ever does set.

The bottom line is that there are several potentially important advantages to using a generic scan interface for initial code retrieval and data analysis, so don’t be afraid to get your feet wet! Since the

generic datastream focuses on the most important inputs and commands, where the bulk of problems occur, and since all PID values reflect their associated sensor states without substitution, you’re less likely to be capsized by a flood of irrelevant data.

As always, checking known-good vehicles will help keep you on an even keel and familiarize you with what “good” looks like. While you may occasionally wind up switching over to an enhanced interface, you’ll likely find that routinely starting in generic using a fast and inexpensive basic scanner results in much greater efficiency.

Whether your shop is large or small, this practice also lets you avoid excessive wear and tear on the more expensive and advanced scanners and keeps them free for those longer-term diagnostic challenges where their enhanced features are actually needed.

This article can be found online at www.motormagazine.com.

Circle #17

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Mandy Concepcion Click to Get the Book Now! Fig-Fuel trim scale showing the entire FT monitor range. Notice the OBD II scale at the top and the older GM scale at the bottom. The equivalent Stoichiometric value of OBD II to GM’s is 0.00% = 128.

In recent years the scan tool, as it became faster and more powerful, has become the equipment of choice for many technicians. It is by far the first tool employed at the start of the diagnostics process and with good reason. The scanner is versatile, with many built in features that no other piece of equipment can match. It is also the only tool that can provide a window into the ECM inner operation and memory functions. In essence, it tells you what the ECM is seeing, regardless of whether it is true or not.

With the scan tool, a whole array of convenient and fast techniques can be employed

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to quickly analyze and diagnose a particular problem. As time goes on, the scanner will see an even broader range of operations, since it is bound to become much faster with newer advances in electronics. It may even get to rival the fastest equipments, like the oscilloscope, at some point-in-time in the future.

This section deals with the proper use of the versatile scan tool. Many different diagnostics techniques will be introduced, as well as ways to make the most out of your scan tool. In the last couple of years the term “PID diagnostic” has been used to denote the ability to diagnose a problem by analyzing the serial data on a scan tool. In fact, given today’s faster scanners, it is possible to perform a great deal of the diagnostics process sitting inside the vehicle. This gives rise to the term “front seat diagnostics”. As much as 70% of the diagnostic work can be perform by the simple correlation of signal data, with the rest employing actual manual testing. As of right now, and probably not for a long while, the scan tool will not replace the trusty VOM or the scope, but its proper use will make things a lot easier due to the time savings. All that translates to money in your pocket.

Serial data communications has been around for a number of years. As far back as the early 1980’s, domestic manufacturers were putting out vehicles with available scan tool data parameters. In the early days, the communication protocols were proprietary in nature, which made it harder for aftermarket equipment makers to come up with affordable scanners for the average technician. Although the need for an OEM scan tool is as important now as ever, a wide range of engine performance and emission faults can be quickly diagnosed by the use of “generic PIDs”. In spite of the fact that the OBD II generic PID serial data stream is many times thought of as being slow and void of any diagnostic importance, this is definitely not so. The generic OBD II protocol works on a request system, which means that the scan tool has to actually ask the ECM for each PID (In OBD II a PID stands for parameter identification). This OBD II request operation contrasts with the OEM communications protocols that work using data packets, whereby, the data stream PIDs is sent in bursts or packets. However, generic OBD II standardized the whole communications process and made it possible to, at least, have access to a minimum of data for diagnostics regardless of make and model. In generic OBD II, by simply reducing the amount of PIDs on the screen a faster data rate can be obtained, since the scanner has to request less data. By combining different and faster data PIDs to form a relationship, a signal correlation can be arrived at. An example is an EGR valve that is commanded on (manually or otherwise) which should have an effect on the MAP sensor. A lack of MAP sensor response is a good indication of a defective or clogged EGR valve, since an opening EGR valve should create a drop in intake vacuum. The same PID strategy is also employed by the ECM when running each drive cycle. The difference is that we can also use these techniques to our advantage when diagnosing a vehicle.

This section will have a somewhat different approach to the rest of the book. An effort has been made to organize the section by the particular problem found and how to diagnose such faults using the different PIDs available to the manufacturer in question. Both OEM (enhanced) and generic information formats (PID data signals) will be implemented in the diagnostics strategies presented here. It is also worth mentioning that in order to attain maximum advantage of these techniques, the use of a graphing-software is highly recommended. If your scan tool has a graphing feature, use it, since it will make the whole process a lot easier. The mind can process graphical representations much faster than just raw numbers. This section has been arranged by using PC generated PID graphing for ease of publishing. Provided that your scanner has a graphing option, the principle is the same. Enjoy the rest of the section.

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FUEL DELIVERY FAULT DETECTION By far, fuel delivery problems account for as much as 60% of all CEL (check engine light) complaints. Modern OBD II (generic and enhanced) as well as late ODB I diagnostic systems offer extensive opportunities for fault detection. These are the parameters that determine fuel delivery, in order of priority.

Base injector pulse-width, as determined by the base fuel-injection-map.

Engine coolant temperature sensor.

Engine RPM. MAP (speed-density) or MAF sensor.

TPS (throttle angle/position).

O2 sensor.

IAT (intake air temperature sensor).

Battery voltage.

External Loads placed on the engine.

The following are the PID associated with fuel related problems.

IAT (intake air temperature) sensor is a secondary analog input to the ECM. Is tells the ECM the temperature of the incoming air. On engines with the IAT screwed into the intake manifold, it is called an air charge sensor. A high air charge sensor temperature reading is a good indication of a clogged exhaust. The reason being is that the backed-up exhaust gasses accumulate on the intake manifold, causing the high air charge sensor temperature reading.

BARO (barometric sensor) is either an analog input or a calculated value to the ECM and can also be considered a main input to the ECM. On vehicles with a separate BARO sensor, the measurement is taken directly. However, the vast majority of fuel systems use the MAP or the MAF sensor for barometric pressure calculations. In MAP systems (speed/density), the BARO value is arrived at by measuring the MAP sensor at either W.O.T. or KOEO. In either case manifold vacuum is nonexistent and the actual reading indicate atmospheric pressure.

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ECT (engine coolant temperature) sensor is an analog input to the ECM. This sensor is a main ECM input, and sets the base injection and ignition characteristics. The ECT sensor also tells the ECM when to go to closed-loop, as soon as a pre selected warm-up temperature has been reached.

ENGINE LOAD is a calculated PID. The ECM takes the RPM, TPS and the MAP/MAF into consideration when calculating the engine load. Some manufacturers (OBD II) report this parameter with a negative load factor included. In other words, if a vehicle is traveling down hill its momentum would be driving the engine, creating a negative load condition. This value would be factored into the overall load PID value, therefore, the normal load values would always be higher than for other manufacturers.

The RPM is a calculated value arrived at from a CRK sensor or the ignition module/pick-up coil input to the ECM. The RPM is a main input and should always be considered when analyzing any PID group.

FUEL TRIMS is a calculated PID and is usually expressed in percentage. The fuel trim is the calculated value of the adjustments performed by the ECM to the base injector pulse. The fuel trim PID is always divided into LTFT (long term fuel trims) and STFT (short term fuel trims). The LTFT are the long-term adjustments performed by the ECM to the base injector pulse. This parameter is an indication of the ECM response to more persistent and influential A/F ratio faults, such as a large vacuum leak (lean) or a punctured fuel pressure regulator (rich). Also, the LTFT only changes value after the STFT has reached its maximum limit and the ECM can no longer adjust the mixture. The LTFT can be thought of as a slow acting parameter that only intervenes when its partner, the STFT, can no longer correct the mixture. The STFT are the short-term adjustments performed by the ECM to the base injector pulse. This PID reacts very fast to changes in the A/F ratio. The ECM will always try and keep the STFT as close to 0.00 % as possible. So long as it can maintain a stoichiometric A/F ratio through smaller corrections to the injector pulse, the STFT will hover at a maximum value of + or – 8 %. In the event that a greater A/F ratio fault exists, the ECM will not be able to correct the problem through smaller corrections and the LTFT will increase, thereby, taking the STFT back to close to 0.00 % again.

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Fig – FUEL TRIM chart depicting the relation between FUEL TRIMS, O2 sensor and RPM. Notice how the ECM tries to keep the STFT close to 0 %. This vehicle was misfiring due to a defective ignition coil. Ignition as well as injector (not pulsing) faults render the exhaust gases with excess O2. The O2 sensor will perceive this as a lean condition, even though there is excess raw fuel being put out by the misfiring cylinders. The O2 sensor is only concerned with the Oxygen content of the exhaust.

About 60 % of all CEL (check eng. light) faults are A/F related. General Motors was the first manufacturer to put out a fuel trim PID. As far back as 1981, GM vehicles were using fuel trim values, which they called “block learn – LTFT and integrator – STFT”.

Older GM vehicles use the lower scale on the chart, which puts 14.7:1 A/F ratio at 128 (OBD II at 0.00%). This older fuel trim scale can still be found today as a scanner PID, thereby, complimenting the newer OBD II generic scale.

Example 1 – An engine (V-6) is operating, at idle, within normal specifications. The STFT are at 3 % (normal) and the LTFT at 2 % (normal). Suddenly an injector goes faulty and starts dripping 20 % more fuel (rich condition). This can be considered a minor fault. At this point in time the O2 sensor goes high (rich) and the ECM compensates by decreasing injector pulse, thereby, sending the STFT to – 5 % or so.

This A/F ratio fault can clearly be controlled by the ECM through minor corrections and will probably not change the LTFT values.

Example 2 – The same engine is again operating normally, with the STFT and LTFT values within proper range. Suddenly the intake manifold gasket ruptures and a large vacuum leak is created. At this time, the O2 sensor voltage goes low (lean) causing the ECM to increase injector pulse time to try and correct the fault. This action raises the STFT to its maximum of 25 %. After a short time, the ECM samples the O2 sensor and still sees a low voltage. The ECM then increases or adds more on-time to the injector pulse, again trying to correct for the lean condition. This action will raise the

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LTFT from 2 % (normal) to 10 % for the first time. This cycle of A/F correction will continue until the mixture is brought back to stoichiometry and the O2 sensor starts switching again, in which case the LTFT would stay high and the STFT would go back close to 0 %. In the event that the vacuum leak becomes too large, the STFT as well as the LTFT would reach their maximum positive values and the ECM will set a faulty code for a lean condition. At this point, the STFT and LTFT would be at around 25 % to 35 % or maximum, depending on the manufacturer. The one important fact about fuel trims to remember is that even if they may be off, the A/F ratio is still at stoichiometry or 14.7:1. The fact that the fuel trim values are off only means that the system is operating outside the base injection map, by the same factor. The following graph shows the fuel trims in action.

As a last note regarding fuel trims, this parameter re-zeroes under different load conditions. Every time the ECM switches to a different cell, the fuel trims re-zeroes and relearns a different adaptive value.

NOTE: This training blog is taken from our book "Diagnostic Strategies of Modern Automotive Systems". For further -how to test- instructions visit our book section on our website

Copyright © Mandy Concepcion, Automotive Diagnostics and Publishing

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Using a Scan Tool to Diagnose Your Car por Popular Mechanics

It’s state inspection time and you’re ready to leave bright and early for the inspection station with the family’s ’98 minivan. You’re starting the day in a less than jovial mood because your daughter said “the light came on” last night on the way home. She said she threw a few dollars of gas into the tank to make it home. Turns out your annoyance is misplaced. Sure enough, the light’s on all right, but it’s not the fuel warning, it’s the Check Engine warning. You stop for gas anyway, and then you pull into the inspection lane.

Well, full tank or not, the minivan does not pass muster.

Now what? This Instructable will help you use scan tools to diagnose your car's problems. You can do the basics yourself before taking the car in to a mechanic.

This project was originally published in the August 2001 issue of Popular Mechanics. You can find more great projects at Popular Mechanics DIY Central.

Paso 1: Use an OBD II

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This is a late-model vehicle with what’s known as OBD II, the second-generation on-board diagnostic system that replaced OBD I starting in 1994. It’s industry-wide and federally mandated. One of the problems with OBD II for the do-it-yourselfer is that you can’t get trouble codes by counting the blinks on the Check Engine light like you can on earlier computer-controlled vehicles. You could take your minivan into a high-tech shop, where the minimum charge for diagnosis and inspection could run you somewhere into three figures. Or you can learn about OBD II yourself, but you will need a piece of diagnostic equipment that you probably don’t have—an OBD II scan tool.

If the Check Engine light came on, it should be no surprise that the vehicle failed an emissions test. With OBD II, that light comes on only if there’s a failure that significantly affects emissions. That makes the scan tool even more important since it will reveal a lot of the problems that do not cause the warning light to come on.

With many problems, the light stays on after the repair is made and the code remains in the computer memory for a certain number of ignition on/off cycles. Your daughter didn’t tighten the gas cap correctly, causing a code for the evaporative emissions system to set. Eventually the light will go out and the code will self-erase, perhaps after the next time you start and stop the car. You also can use the scan tool to erase it immediately.

With many other problems, however, the only way to turn off the light and erase the code is with the scan tool. Just a warning: If you erase trouble codes with a scan tool or disconnect the battery for any reason, you also erase the computer’s continuous monitoring system. So if you take your car in for a state inspection before enough normal driving, the computer might not have completed all its tests, and your car will fail inspection for that reason.

The OBD II scan tester not only will enable you to find answers to the simpler problems, but will tell you into

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what areas the seemingly more complicated ones fall. Then you will have a better understanding of what the technician is (or should be) looking for.

Paso 2: Cracking the Code With an OBD II scan tool you also can read a certain amount of engine operating data: typically rpm, ignition timing, fuel-injection calibrations, readings from a variety of sensors (such as the oxygen, throttle position, barometric and mass airflow sensors), a “calculated load” value and sometimes switch position signals. OBD II also includes a “capture” mode, in which you can use the scan tool to take a “snapshot” of what the sensors were reading at the exact instant a driveability hiccup occurred.

Paso 3: Sensor Scan

With enhanced scan tool capability, you can discover problems that do not trigger the engine-warning light.

For example, we recently turned up a generic PO713 code on a late-model car. This is listed in the shop manual as “transmission fluid temperature sensor circuit—high input.” If the transmission fluid is running very hot, the transmission could completely fail, and quickly.

A scan tool could save a lot of worry and effort if it has enhanced diagnostics. You can do much of the troubleshooting from the driver’s seat the way we did. First we cleared the code with a simple push of a button on the tester. Then we rechecked: the code came back quickly. We cleared it again and looked at the

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reading that was coming from the transmission temperature sensor to the powertrain computer. It was 131˚ F, nothing abnormal.

The problem apparently was in the sensor or the circuit, possibly a bad connection. The wiring was good and when we started poking around, we found physical damage that clearly indicated the problem was a defective sensor.

Paso 4: Scan Tool Choices

If you have a late-model vehicle, you have OBD II. However, just because it’s generic, and the wiring connector from any OBD II scan tool will plug into your vehicle, doesn’t mean any OBD II scan tool will work on your car. The Europeans are the problem, as the latest ones (1998 and later) require a software upgrade.

Korean cars are also problematic, and how well they work with any given scan tool needs to be investigated on a case-by-case basis.

The OTC Mind Reader for OBD I can be upgraded with an additional chip to read generic OBD II in domestic, Japanese and earlier European models (but not the newest Europeans).

The Actron ScanTool for OBD I can be updated to the same level of OBD II as the OTC Mind Reader with a plug-in cartridge (or you can buy an OBD II-only model).

AutoXray produces a programmable scan tool. Although it doesn’t have the OBD I Chrysler command tests of the Mind Reader, it is the one home mechanic’s scan tool we’ve tested to date that covers all generic OBD II models (including the Europeans) with more on the way. The software will be sold over the Internet. You’ll be able to store it on your personal computer and then download it to your scan tool via a cable available from

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the manufacturer.

Any AutoXray scan tool is designed to be upgraded electronically, from one-make OBD I coverage through the latest models. Although the professionals have had all this software (and a lot more) in their scan tools, you have to wait for it in the general consumer market. Other scan tools may be upgraded to enhanced status and beyond with new cartridges, CD-ROM or via the Internet.

Although Actron has a line of OBD II scan tools, its top tester for car owners is the Actron CP9087, a simple code reader with read-codes and code-erase buttons. You get no sensor readings or other data items. It’s a low-cost device (under $200) that comes with a good assortment of wire leads for making test connections— including a back-probe adapter that has a thin, curved metal terminal. This terminal lets the probe slip through a water-sealed connector to reach a wiring terminal for a test connection.

[As of 2001] OBD II is entering its sixth full year and the earliest vehicles that have this system are off warranty. OBD II is complex and we’ve given you just a basic introduction. The OBD II powertrain computer is getting a lot better at finding problems and logging codes. But, the computer won’t tell you a thing unless you hook up a scan tool.

Paso 5: How OBD II Transmits Data

Today's powertrain computers are at the heart of a vehicle's communications network, circulating information from switches and sensors to the other computers that control antilock brakes, air conditioning, transmission, suspension and safety systems. The powertrain computer is also in charge of systems that affect engine emissions, so the information it processes has to be available for evaluation by a technician. That information travels along a wire to a standard 16-terminal diagnostic connector (although, generally, fewer than a halfdozen terminals are live in any given vehicle). Because manufacturers do not all use the same data transmission protocols, the scan tool must be programmed to recognize which one is being used.

Fortunately, there has been some standardization, but we're not down to one transmission protocol for all, hence the problem with late-model European cars (including the Cadillac Catera). There are four different socalled stand-and-data pins in the standard connector, and at least four different types of data transmissions that could be used, plus enhanced version sof the standard stuff (other piins are available for additional manufacturer-specific data, such as vehicle diagnostic systems for a/c and ABS).

As anyone with a household PC knows, "plug and play" doesn't always work, and OBD II scan tools can encounter compatibility problems. Some European and Korean cars don't always work when they're supposed to. How can you tell? Checking a scan tool manufacturer's web site for updates is the way to keep your tool current.

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OBDII GENERIC PID DIAGNOSIS

BY KARL SEYFERT

S

ome scan tools call it the global OBD II mode, while others describe it as the OBD II generic mode. The OBD II generic mode allows a technician to attach his scan tool to an OBD II-compliant vehicle and begin collecting data without entering any VIN information into the scan tool. You may need to specifically select “OBD II Generic” from the scan tool menu. Some scan tools may need a software module or personality key before they’ll work in generic OBD II test mode.

The original list of generic data parameters mandated by OBD II and described in SAE J1979 was short and designed to provide critical system data only. The useful types of data we can retrieve from OBD II generic include

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short-term and long-term fuel trim values, oxygen sensor voltages, engine and intake air temperatures, MAF or MAP values, rpm, calculated load, spark timing and diagnostic trouble code (DTC) count. Freeze frame data and readiness status also are available in OBD II generic mode. A generic scan tool also should be able to erase trouble codes and freeze frame data when commanded to do so.

Data coming to the scan tool through the mandated OBD II generic interface may not arrive as fast as data sent over one of the dedicated data link connector (DLC) terminals. The vehicle manufacturer has the option of using a faster data transfer speed on other DLC pins. Data on the generic interface also may not be as complete as the information you’ll get on many manufacturer-

Photo: Karl Seyfert

A wealth of diagnostic information is available on late-model OBD II-compliant vehicles, even when ‘enhanced’ or ‘manufacturer-specific’ PIDs are not accessible. It doesn’t take much to use this information to its best advantage.

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Photos: Karl Seyfert

OBD II GENERIC PID DIAGNOSIS

Here’s a basic scanner display showing OBD II generic PIDs. Slow-changing PIDs like IAT and ECT can be followed fairly easily in this format, but it’s difficult to spot glitches in faster moving PIDs like Spark Advance.

Mode 1: Show current data Mode 2: Show freeze frame data Mode 3: Show stored trouble codes Mode 4: Clear trouble codes and stored values Mode 5: Test results, oxygen sensors Mode 6: Test results, noncontinuously monitored Mode 7: Show pending trouble codes Mode 8: Special control mode Mode 9: Request vehicle information Modes 1 and 2 are basically identical.

Mode 1 provides current information, Mode 2 a snapshot of the same data taken at the point when the last diagnostic trouble code was set. The exceptions are PID 01, which is available only Photo courtesy Snap-on Diagnostics

specific or enhanced interfaces. For example, you may see an engine coolant temperature (ECT) value in degrees on the OBD II generic parameter identification (PID) list. A manufacturerspecific data list may display ECT status in Fahrenheit or Celsius and add a separate PID for the ECT signal voltage.

In spite of these and other limitations, OBD II generic mode still contains many of the trouble codes, freeze frame data and basic datastream information needed to solve many emissions-related issues.

There are nine modes of operation described in the original J1979 OBD II standard. They are:

This scan tool also allows the user to graph some PIDs, while continuing to display the others in conventional numeric format. Due to OBD II’s refresh capabilities on some vehicles, it’s best to limit your PID choices to those directly related to your diagnostic approach.

This photo illustrates how far PID data collection and display have come. Several hundred thousand techs are still using the original Snap-on “brick” (on the left), which displays a limited amount of PID data on its screen. Scrolling up or down revealed more PIDs. The color version on the right brought graphing capability to the brick, and extended the product’s life span by several years.

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in Mode 1, and PID 02, available only in Mode 2. If Mode 2 PID 02 returns zero, then there’s no snapshot and all other Mode 2 data is meaningless. Vehicle manufacturers are not required to support all modes. Each manufacturer may define additional modes above Mode 9 for other information.

Most vehicles from the J1979 era supported 13 to 20 parameters. The recent phase-in of new parameters will make OBD II generic data even more valuable. The California Air Resources Board (CARB) revisions to OBD II CAN-equipped vehicles have increased the number of potential generic parameters to more than a hundred. Not all vehicles will support all PIDs, and there are many manufacturer-defined PIDs that are not included in the OBD II standard. Even so, the quality and quantity of data have increased significantly. For more information on the new PIDs that were added to 2004 and later CAN-equipped vehicles, refer to Bob Pattengale’s article “Interpreting Generic Scan Data” in the March 2005 issue of MOTOR. A PDF copy of the article can be downloaded at www.motor.com.

Establish a Baseline If you’re repairing a vehicle that has stored one or more DTCs, make sure you collect the freeze frame data before erasing the stored codes. This data can

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OBD II GENERIC PID DIAGNOSIS

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Photo courtesy Injectoclean

Photo courtesy SPX/OTC

Screen capture: Jorge Menchu

IAC counts look too high or be used for comparison after too low? Compare data items your repairs. The “before” to known-good values you’d freeze frame shot and its PID expect to see for similar opdata establish the baseline. erating conditions on similar As you begin your diagnovehicles. sis, correct basic problems Check short-term fuel first—loose belts, weak battrim (STFT) and long-term teries, corroded cables, low fuel trim (LTFT). Fuel trim coolant levels and the like. is a key diagnostic parameter The battery and charging sysand tells you what the comtem are especially important, puter is doing to control fuel due to their effect on vehicle delivery and how the adapelectronics. A good battery, a tive strategy is operating. properly functioning alternaSTFT and LTFT are extor and good connections at pressed as a percentage, with power and ground circuits the ideal range being within are essential. You can’t asThe Snap-on MODIS is a combination scanner, lab/ignisume that OBD II will detect tion scope, DVOM and Troubleshooter. In scanner mode, ±5%. Positive fuel trim pera voltage supply problem that MODIS can graph several parameters simultaneously, centages indicate that the can affect the entire system. as seen in this screen capture. Remember, although powertrain control module If you have an intermittent these may look like scope patterns, the reporting rate (PCM) is attempting to enrichen the fuel mixture to problem that comes and for PID data on a scanner isn’t nearly as fast. compensate for a perceived goes, or random problems that don’t follow a logical pattern, check down the battery voltage and the results lean condition. Negative fuel trim perthe grounds for the PCM and any other of any simple tests, such as fuel pressure centages indicate that the PCM is atcontroller in the vehicle. or engine vacuum. Look at the Readi- tempting to enlean the fuel mixture to If the basics check out, focus your di- ness Status display to see if there are compensate for a perceived rich condiagnosis on critical engine parameters any monitors that aren’t running to tion. STFT will normally sweep rapidly between enrichment and enleanment, and sensors first. Write down what you completion. while LTFT will remain more stable. If find; there’s too much information to either STFT or LTFT exceeds ±10%, keep it all in your head. Add any infor- Datastream Analysis mation collected from the vehicle own- Take your time when you begin looking this should alert you to a potential er regarding vehicle performance. Jot at the live OBD II datastream. If you se- problem. lect too many items at one time, the scan tool update will slow. The more PIDs you select, the slower the update rate will be. Look carefully at the PIDs and their values. Is there one line of data that seems wrong? Compare data items to one another.

Do MAP and BARO agree key on, engine off (KOEO)? Are IAT and ECT the same when the engine is cold KOEO? The ECT and IAT should be within 5°F of each other. ECT should reach operating temperature, preferably 190°F or higher. If the ECT is too low, the PCM may richen the fuel mixture to compensate for a (perceived) coldengine condition. IAT should read ambient temperature or close to underhood When scan tool screen real estate is temperature, depending on the location limited, porting the scan tool into a laptop or desktop PC allows you to of the sensor. graph more PIDs simultaneously.

An on-screen description of the PID Is the battery voltage good KOEO? The PC’s much larger memory cadisplayed below the graphing data Is the charging voltage adequate when pacity also makes it possible to colmay help you to understand what lect PID data in movie format for you’re looking at, and avoid misunder- the engine starts? Do the MAP and BARO readings seem logical? Do the later playback and analysis. standings with measurement units.

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Screen captures: Jorge Menchu

OBD II GENERIC PID DIAGNOSIS

Graphs aren’t the only way to display PID data. Once transferred to the PC with its greater screen real estate, PID data can be converted to formats that relate to the data. A red thermometer scale is much easier to follow than changing numbers on a scan tool.

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The PCM uses this information to calculate the amount of fuel that should be delivered to achieve the desired air/fuel mixture. Check the MAF sensor for accuracy in various rpm ranges, including wide-open throttle (WOT), and compare it with the manufacturer’s recommendations.

When checking MAF sensor read-

Screen capture courtesy Bosch Diagnostics

Determine if the condition exists in more than one operating range. Check fuel trim at idle, at 1500 rpm and at 2500 rpm. If LTFT B1 is 20% at idle but corrects to 5% at both 1500 and 2500 rpm, focus your diagnosis on factors that can cause a lean condition at idle, such as a vacuum leak. If the condition exists in all rpm ranges, the cause is more likely to be fuel-related, such as a bad fuel pump, restricted injectors, etc.

Fuel trim can also be used to identify which bank of cylinders is causing a problem on bank-to-bank fuel control engines. For example, if LTFT B1 is 25% and LTFT B2 is 5%, the source of the problem is associated with B1 cylinders only, and your diagnosis should focus on factors related to B1 cylinders only.

The following parameters could affect fuel trim or provide additional diagnostic information. Also, even if fuel trim is not a concern, you might find an indication of another problem when reviewing these parameters: Fuel System 1 Status and Fuel System 2 Status should be in closed-loop (CL). If the PCM is not able to achieve CL, the fuel trim data may not be accurate.

If the system includes one, the mass airflow (MAF) sensor measures the amount of air flowing into the engine.

PC-based scan tools excel at capturing and displaying large amounts of PID data for later analysis. Graphing the data, then analyzing it on-screen, may allow you to spot inconsistencies and provides an easy method for overlaying similar or related PID data.

Here’s a peek at some of the additional PID data that’s available on latemodel vehicles. This screen capture was taken from a CAN-enabled 2005 vehicle, and includes PIDs for EVAP PURGE, FUEL LEVEL and WARM-UPS, as well as familiar PIDs like BARO. This much PID data in generic mode should aid in diagnosis when manufacturerspecific PID data is not available.

ings, be sure to identify the unit of measurement. The scan tool may report the information in grams per second (gm/S) or pounds per minute (lb/min). Some technicians replace the sensor, only to realize later that the scan tool was not set correctly. Some scan tools let you change the units of measurement for different PIDs so the scan tool matches the specification in your reference manual. Most scan tools let you switch easily between Fahrenheit and Celsius temperature scales, for example. But MAF specs can be confusing when the scan tool shows lb/min and we have a spec for gm/S. Here are a few common conversion formulas, in case your scan tool doesn’t support all of these units of measurement: Degrees Fahrenheit 32 5/9 Degrees Celsius Degrees Celsius 9/5 + 32 Degrees Fahrenheit lb/min 7.5 gm/S gm/S 1.32 lb/min The Manifold Absolute Pressure (MAP) Sensor PID, if available, indicates manifold pressure, which is used by the PCM to calculate engine load.

The reading is normally displayed in inches of mercury (in./Hg). Don’t confuse the MAP sensor parameter with intake manifold vacuum; they’re not the same. Use this formula: barometric

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pressure (BARO) MAP intake manifold vacuum. For example, BARO (27.5 in./Hg) MAP (10.5) intake manifold vacuum (17.0 in./Hg). Some vehicles are equipped with only a MAF sensor, some have only a MAP sensor and some are equipped with both.

The PIDs for Oxygen Sensor Output Voltage B1S1, B2S1, B1S2, etc., are used by the PCM to control fuel mixture and to detect catalytic converter degradation. The scan tool can be used to check basic sensor operation. The sensor must exceed .8 volt and drop below .2 volt, and the transition from low to high and high to low should be quick.

A good snap throttle test will verify the sensor’s ability to achieve the .8 and .2 voltage limits. If this method doesn’t work, use a bottle of propane to manually richen the fuel mixture to check the oxygen sensor’s maximum voltage output. To check the sensor’s low voltage range, simply create a lean condition and check the voltage.

Remember, your scan tool is not a lab scope. You’re not measuring the sensor in real time. The PCM receives the data from the oxygen sensor, processes it, then reports it to the scan tool. Also, a fundamental OBD II generic limitation is the speed at which that data is delivered to the scan tool. In most cases, the fastest possible data rate is approximately 10 times a second, with only one parameter selected. If you’re requesting and/or displaying 10 parameters, this slows the data sample rate, and each parameter is reported to the scan tool just once per second. You can achieve the best results by graphing or displaying data from each oxygen sensor separately.

If the transition seems slow, the sensor should be tested with a lab scope to verify the diagnosis before you replace it.

The Engine Speed (RPM) and Ignition Timing Advance PIDs can be used to verify good idle control strategy.

Again, these are best checked using a graphing scan tool. Check the RPM,

Vehicle Speed Sensor (VSS) and Throttle Position Sensor (TPS) PIDs for accuracy. These parameters can also be used as reference points to duplicate symptoms and locate problems in recordings.

Most PID values can be verified by a voltage, frequency, temperature, vacuum or pressure test. Engine coolant temperature, for example, can be verified with a noncontact temperature tester, while intake manifold vacuum can be verified with an accurate vacuum gauge. Electrical values also should be tested with a DVOM. If the electrical value exists at the sensor but not at the appropriate PCM terminal, then the component might be experiencing a circuit fault.

Calculated Values Calculated scan tool values can cause a lot of confusion. The PCM may detect a failed ECT sensor or circuit and store a DTC. Without the ECT sensor input,

Circle #31

September 2007

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OBD II GENERIC PID DIAGNOSIS the PCM has no idea what the coolant temperature really is, so it may “plug in” a temperature it thinks will work to keep the engine running long enough to get it to a repair shop. When it does this, your scanner will display the failsafe value. You might think it’s a live value from a working sensor, when it isn’t.

Also be aware that when a component such as an oxygen sensor is disconnected, the PCM may substitute a default value into the datastream displayed on the scan tool. If a PID is static and doesn’t track with engine operating conditions, it may be a default value that merits further investigation.

Circle #32

Circle #33

Circle #35

Circle #34

Graphing Data If you’ve ever found it difficult to compare several parameters at once on a small scan tool screen, graphing PIDs is an appealing proposition. Graphing multiple parameters at the same time can help you compare data and look for individual signals that don’t match up to actual operating conditions.

Although scan tool graphing isn’t equivalent in quality and accuracy to a lab scope reading, it can provide a comparative analysis of the activity in the two, three, four or six oxygen sensors found in most OBD II systems.

Many scan tools are capable of storing a multiple-frame movie of selected PIDs. The scan tool can be programmed to record a movie after a specific DTC is stored in the PCM. Alternatively, the scan tool movie might be triggered manually when a driveability symptom occurs. In either case, you can observe the data or download it and print it later. Several software programs let you download a movie, then plot the values in a graphical display on your computer monitor.

Make the Most of What You’ve Got Take the time to learn what your scan tool will do when connected to a specific make or model. Do your best to gather all relevant information about the vehicle system being tested. That way you can get the most out of what the scan tool and PCM have to offer.

The OBD II system won’t store a DTC unless it sees (or thinks it sees) a problem that can result in increased emissions. The only way to know what the PCM sees (or thinks it sees) is to look through the window provided by the scan tool interface.

You have a DTC and its definition.

You have freeze frame data that may help you zero in on the affected component or subsystem. PIDs have already provided you with additional clues about the operation of critical sensors.

Keep your diagnosis simple as long as you can. Now fix the car.

Visit www.motor.com to download a free copy of this article.

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Driveability Diagnostics, OBD I & II

By Steve Zack - SPX Technical Trainer and Chuck Eaves -Technical Specialist, JA Echols & Assoc Since the dawn of on-board diagnostics (OBD) in motor vehicles, the process of diagnosing driveability problems are the same as always, and very different, too. When OBD I evolved into OBD II in 1996, the electronic part of diagnosing driveability problems became a little easier. This is because the electronic network on OBD II vehicles became much more comprehensive and changed almost all mechanical functions that controlled the powertrain into electro/mechanical functions.

There are three indispensable tools to diagnose OBD system problems and make the proper repairs.

These tools and how to use them will be explored in some detail.

Scan Tool Diagnostics The first tool we’ll talk about is the scan tool. In general terms, there are two types of “scan tools”. One is referred to as a Code Reader. These simple electronic tools are useful and will read and erase all OBD emissions codes. Some will also give the code description, but not all code readers do this. A true scan tool, however, will read and clear OBD codes, and will do the same on “enhanced” and “subsystem” codes. These enhanced codes are OEM-specific, with OEM assigned numbers. These codes cover the entire electronic control spectrum beyond purely emissions. Beyond driveability, the codes will cover the HVAC, IPC, BCM, ABS, SRS, and electronic-bus communication systems. The true scan tool will also do many other important and useful things, and these will be discussed later.

Most of you have already noted the superior functionality of the OBD II system compared to the OBD I system. Some of the enhanced capability of the OBD II system will be found on OBD I. Most, however, will not. As already mentioned, OBD II was adopted across the board in 1996. You will find a couple of models of each manufacturer that introduced OBDII as early as 1994. These early OBD II vehicles were early production models, and usually employed both the OBD II 16 pin connector and the vehiclespecific connector to access the other systems.

Just remember, the scan tool reads and reports to you what the vehicle’s computer system is doing and saying. If the computer system in the vehicle can’t know or do a certain thing, like reading ignition kV, the scan tool cannot give you this information. The scan tool, then, is the interface between you and the vehicles’ computer system.

There are two other tools, both of which have been around for quite a while, which are very important in diagnosing OBD problems. One is the technician; in other words, YOU. There will never come a day when the technician will not be absolutely essential to diagnose and repair OBD problems. No scan tool can fix the vehicle, and the scan tool will often only point you to the problem area. Your job is secure if you are willing to keep up with ever-advancing technology. This requires an on-going investment in education and tools. This will never change. Scan tools don’t fix cars, you do! If you do your job well, you will make a very nice living fixing everything, but nothing more, than your customer’s vehicle requires.

Part of your investment in your diagnostic future is in updating your scan tool. The electronic world will never stop moving and improving. Do not get angry with your scan tool distributor for offering you the latest update when it becomes available. Out-of-date software or hardware is like having only three points on your Philips screwdriver. It will still work, sort of, for a while maybe. Don’t wait. Update your tool every chance the manufacturer gives you. You’ll appreciate the difference the first time you use your tool, especially if you’ve just updated your OTC Pegisys, Genisys, or Nemisys . The functionality improvements OTC has added to the additional diagnostic information year-to-year in the OTC family of scan tools are nothing short of remarkable.

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The third and last electronic diagnostic tool that we will address is the oscilloscope, or “scope” for short. Simply put, the purpose of a scope is to put a picture on a screen of the electrical activity that is going on in whatever you are testing. This picture is a constantly moving line trace, or graph, called a “pattern”. The scope info on the screen is “live”, not processed as with a scan tool. This fact makes scope information more accurate and more current than scan tool data, which first has to be processed by the vehicles computer, then again by the scan tool. Scan tool data is almost always reliable, but should be verified by a scope (or a digital multi-meter) before the repair is made. Otherwise, you may find yourself reading codes and pulling parts, over and over. This approach will be very unpopular with your customer, and will cost you money.

A high-quality scope can be expensive, and many techs simply don’t know how to use one. The Genisys and Pegisys, by OTC , are very easy to use, full-function scan tools with a 2 or 4-channel lab/engine analyzer scope. The price is surprisingly reasonable, especially when compared to the competition. OTC’s scope module for the Genisys is a full-function 4-channel 4-color scope that accurately presents all automotive voltage from mV through kV levels. The new OTC Pegisys has an ultra-high speed 2 channel scope built in, with all the advanced capability of the Genisys ’ 4 channel model, but with 2 channels for easier operation.

Before beginning the in-depth discussion of how to best use your scan tool, a few basic understandings are in order. You ASE Master Techs out there, just bear with us a little bit.

OBD I codes (early 1980’s through 1995) use two and three digit numbers without letters. They are all manufacturer assigned. OBD II codes (1996 up) consist of a letter followed by four numbers. There are four different letters for OBD II, and they are as follows: P – Powertrain codes, meaning engine and transmission. All emission codes start with P. B – body codes C – chassis codes U – communication-bus/network codes In the “P” code group, if the first number is “0” (zero), all the codes are “generic”. This means that any light truck and car sold in America from 1996 on share the same P0 codes. The codes mean the exact same thing on all vehicles. P1 codes, however, are OEM assigned, and mean whatever the manufacturer wants them to mean as long as they are powertrain related.

The meaning of the second number in the P0 codes is as follows: 1 – Fuel metering, things like MAF, MAP, O2 sensors, etc.

2 – Fuel metering, but injector and injector circuit only 3 – Misfire and ignition 4 – Emission controls, like EVAP, EGR, CAT, etc.

5 – Vehicle and idle speed control 6 - and 7 – Transmission The last two numbers give you the specific identification within the general system. Example: P0101.

This means powertrain, OBD II emissions, fuel metering, mass air flow meter.

In the OBD II system, there are three types of codes. These are “Current”, “Pending”, and “History”. A current code will set the check engine light after one, two, or three “consecutive similar trips”, depending on which Monitor detects the problem. The conditions that the Monitor evaluates before deciding to illuminate the Check Engine Light are called “Enabling Criteria”. This fancy term simply refers to the process the vehicles’ computer goes through in deciding whether the problem is reoccurring and serious enough to set a code and turn on the light.

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The “check engine light” is correctly called a “MIL”, or “Malfunction Indicator Light”. We’ll call it a MIL (not MIL light). The MIL only illuminates if the problem is a P code, emissions related. All “check engine light” codes are correctly called “diagnostic trouble codes”, or “DTC’s”. Let’s just use “codes” for DTC. It’s easier.

Current, Pending, and History codes (OBD II only) Many current codes will set the MIL when it comes out of Pending and into Current. If the MIL illuminates as a result of an emissions code, a History code will be recorded, and a “Freeze Frame” recording will be stored. A Freeze Frame recording saves one frame of data on several PID items such as RPM, VSS, MAP and/or MAF, IAT, ECT, etc. Accessing the Freeze Frame recording will give you an idea of just what the vehicle was doing when the MIL set. DO NOT clear your codes first. All Pending and Freeze Frame info will disappear when your code/s are cleared.

If you are using the OTC Pegisys, Genisys or Nemisys , you can save the codes and Freeze Frame to tool memory before you clear your codes. The Pegisys and Genisys will automatically record a datastream list if a MIL sets while you are communicating with the vehicle. The Genisys and Nemisys recording is a staggering 1,000 frames, approximately 82 before, and 918 after the MIL illuminates, and the Pegisys can record an infinite number of frames. This Automatic Data Stream Recording will not disappear when the codes are cleared, and can be saved to your OTC Pegisys or Genisys, printed, transferred to a USB jump drive, and/or your shop computer.

NOTE: If the battery in the vehicle is disconnected for any reason, the PCM will loose any Code information it had stored. Of course, all radio, mirror, seat, and HVAC memory will be cleared also. I recommend a Memory Saver if the vehicles’ battery has to be disconnected.

Your tool and equipment distributor has a variety of these devices available, at a reasonable cost. Be sure to get one with enough amperage to last as long as the vehicles’ battery is to be disconnected.

A Pending Code can erase itself before the light comes on if the problem goes away and stays away for two or three consecutive similar trips. If this happens, no History code or Freeze Frame will be stored.

A History code is the medium and long-term storage of a Current code in the computers’ memory, and is strictly for the use of the technician in analyzing a new problem. The History code provides the tech a record of code activity in the recent past. The History code is not an active code; it is a recorded event.

The History code carries no Freeze Frame data with it.

The History code will self-clear from the computers’ memory after 80 trips (for Continuous Monitors), or 40 trips (for Non-Continuous Monitors). However, some vehicles’ software will keep the History codes for 256 key-starts. Chrysler is an example of key-start count for History code memory.

There are four specific levels of codes. These levels indicate the priority of the code, and are explained as follows. Of course, a priority letter is only assigned to a code when there are multiple codes at the same time.

Type A codes: The MIL will be triggered on the first trip with the type A codes, and will record a freezeframe record. Type A’s should be repaired first.

Type B codes: The MIL will trigger on the second or third trip with Type B, and a freeze-frame will be recorded. Type B codes should be addressed after the type A codes have been dealt with.

Type C codes: Non-emissions related, these codes will store a History record, and should have a third place priority.

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Type D codes: Non-emissions related, and will not store a freeze frame or a History record. Repair these codes last.

Code Categories There are three categories of codes within the OBD II system. They are Electrical, Mechanical, and Rational. Each type of code is specific in its setting criterion.

Electrical codes deal with the electrical circuit and its supply source. These codes can be set by a below-standard voltage supply and ground issues, as well as actual circuit failures. An Electrical code will set when extreme or sudden changes in voltage data is noticed when no changes in engine load or circuit operation are observed. An example is a TP sensor which suddenly shows a voltage of less than .2v. This type of fault is monitored by the Comprehensive Components Monitor, and therefore sets a code instantly upon parameter failure.

Mechanical codes deal with devices having a mechanical function, such as the passing of fluids or opening and closing of passages. A good example is an EGR passage that may be partially plugged, not allowing the correct volume of exhaust gas to flow. This mechanical code is monitored by the EGR Readiness Monitor. This Monitor uses several EVAP and engine sensors to watch for a change in value outside the pre-set parameters, setting a code on the second trip cycle.

Rational codes are set when a sensor does not meet its criterion of operation. An example of a Rational code would be the MAF sensor showing a very high volume of air flow with low engine RPM, a small throttle opening, and no indication of an increase in engine load. This type of MAF PID would indicate an out-of-calibration MAF based on what the other sensors show. In this example, the MAF sensor would not be used by the PCM for fuel control.

Each of the above three code types is tested by the Readiness Monitor dedicated to the particular emissions system involved. When a component fails to meet the standard set by the manufacturer during its trip cycle, the component is further monitored for a given period of time. When the component parameters are still not met after the drive cycle is satisfied, a failure is recorded and the MIL is illuminated. The particular components’ parameters are recorded and shown in the “Component Parameters” (Mode 6) section of “Special Tests”.

Failure Type Byte DTC There is now a new DTC numbering system in town. An example of this new system is “P0110:1C-AF”.

The additional digits at the end of the DTC indicate the “Failure Type Byte”. When a FTB appears on the end of the DTC it will be used by the PCM to give more information about the failure. Many DTC numbers provide enough of a description with the alpha and 4 digits. However, many do not and as a result it is sometimes difficult to determine the exact failure from the DTC without a lot of diagnostic work. An FTB will be added to certain DTC’s when necessary to add a more detail description of the failure leading you to a simpler diagnosis. In the past, P0110 indicated an ‘Intake Air Temperature Sensor Circuit” which may be problems with any of the wiring between the sensor and the PCM, or the sensor itself are at fault. With the new indicator at the end of the fault code (1C-AF), the DTC now gives a more complete description of the failure. This example is indicating the Intake Air Temperature Sensor itself is out of range.

Monitors (OBDII only) Another significant difference between OBD I and II is the onboard diagnostic testing called “Monitors”.

The Monitors are active tests of up to eleven electronic systems in the OBD system. Not all OBDII vehicles support all 11 Monitors, however. In fact, two Monitors in particular have never been activated.

One is the A/C Monitor, planned before r-134 became the standard mobile refrigerant used in the US. R134 was judged to be much less harmful to the atmosphere compared to r-12, so the AC monitor has never been used.

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The other Monitor never activated is the Heated Catalyst. The engineering principal behind heating the catalytic converter quickly is the same as heating the O2 sensors: get the cat and the O2 sensors on line within seconds, not minutes. However, the electrical current required to get a catalytic converter up to operating temperature with a heater, and within seconds, is still waiting on the 42v system. This relatively high-voltage electrical system is sure to become a reality one day, but technical and cost challenges have to be overcome first.

The Monitors that the OBDII system runs are divided into two groups: Continuous, and Non-Continuous.

The Continuous Monitors run their diagnostic tests on three emission control systems continually as long as we have key-on, engine running. These Monitors are: 1 - Misfire 2 - Fuel System 3 - Comprehensive - The Comprehensive Monitor looks for open or shorted circuits, and data that is out of range. All OBDII compliant vehicles run these three Monitors.

The Non-Continuous Monitors run their diagnostic tests once per trip, but not continuously. These Monitors include: 1 – Oxygen sensor 2 – Oxygen sensor heater 3 – Catalyst 4 – Heated catalyst (not used) 5 – EGR system (not universally used) 6 – EVAP system 7 – Secondary air system (not universally used) OBD II compliant vehicles run all Continuous Monitors and most of the Non-Continuous monitors. A very few OBD II engines do not need an EGR valve, so do not run that Monitor. Almost all Californiacompliant systems use secondary air systems, so they will run that Monitor. Most Federal-compliant engines do not.

As already stated, when a MIL is illuminated as a result of an emissions related code, an action called “Freeze Frame” is initiated by the PCM. A freeze frame is a snapshot of 8 or 10 PID items. These recordings are required by EPA regulation to capture loop status (open or closed), engine load, coolant temperature, and fuel trim, manifold vacuum (MAP), RPM, and DTC priority. Some PCM’s may add vehicle speed, throttle position, ignition advance, and trips since the MIL was last cleared.

Advantage Pegisys , Genisys and Nemisys An extremely useful and unique function of the OTC Pegisys , Genisys , and Nemisys is Automatic DTC Datastream Recording . If an OTC scan tool is communicating with the vehicle while in Datastream when a code happens to set, much of the datastream list will be recorded into the Pegisys , Genisys , or Nemisys memory. This recording will not be erased when the codes are cleared and can contain from 11 to 45 or more PID items. Unlike the freeze frame feature of all OBD II PCM’s, the Genisys DTC Datastream recording captures up to 1,000 frames, and the Pegisys an infinite amount of frames, not just one. Every recorded PID can then be graphed and printed to plain paper using a regular HP type inkjet printer. With available ConnecTech software, all Genisys recordings can be uploaded into your desktop or laptop computer and stored in a file of your choice. The OTC Nemisys offers uploading its recorded information into a computer via an included CD ROM. The OTC Pegisys and Genisys can off-load their recordings onto a USB drive plugged into the tools’ USB port.

OBD System Hardware In both the OBDI and II systems, the vehicles’ computer (PCM from now on) deals with three main pieces of hardware: actuators, sensors, and switches. The PCM receives data from sensors and switches, and commands and actuators accordingly. The PCM is programmed by the manufacturer with

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algorithms to compare what it sees to what it expects to see. A pre-determined difference in expected input or output for a given length of time or trip count will trigger a code. However, the PCM is only so smart! It can’t “think outside of the box” (get it?). Verify the code before you start yanking parts. Your OTC scope or meter is your best friend here.

Incidentally, some literature and technicians refer to the PCM as the ECM (Electronic Control Module).

The two are the same thing. The term ECM, though, is more often used when referring to OBDI systems.

A note of interest: PCM’s from the 1980’s until 1993 or so had their operational memories loaded on a replaceable “PROM”. To correct or update one of these early PCM’s you would replace the existing PROM with the correct new one. As a rule, no special tools are needed, except a wrist grounding strap.

After 1993, the PCM’s had to be reprogrammed or “reflashed”, to correct or update its operation. The new system, known by its SAE number, J2534, is a web-based reflash method. Great news : OTC will offer the J2534-2 multi-vehicle, all modules reflash program as optional software for the OTC Pegisys . .

Modes of Vehicle Operation Both OBD I and II systems operate with two basic modes: open loop then closed loop. Open loop is the mode in use when the engine is first started, and remains in effect until the oxygen sensors (referred to as O2 sensors) begin to operate. In open loop, the fuel mixture is richer than normal so the engine will run smoothly until the ECT (engine coolant temp sensor) tells the PCM the engine has warmed up. This rich mode works like the choke on a carburetor-equipped engine. The HC and CO emissions are very high in this mode, but the O2’s don’t start operating until the exhaust stream reaches 600-650 degrees.

When the O2’s do come online, the vehicle switches to the closed loop mode where the O2’s now control the fuel trim. In cold-weather conditions, it may take up to 15 minutes for the O2’s to come online. It’s even possible for working O2’s to kick out if the vehicle idles for a good while allowing the exhaust stream to cool down below 600 degrees. If this happens, the vehicle will return to open loop, and this may increase exhaust emissions. However, some OEM’s use embedded PCM information to take over fuel trim when and if open loop occurs.

In about 1990, the OEM’s began installing O2 sensors with heaters built into them. These heaters bring the O2 sensors on line in as little as 15 seconds, and they stay on as long as the engine is running. Since the average trip time is quite short in the US, the tailpipe pollution per trip is reduced significantly, as the vehicle stays in closed loop longer.

When OBD II became law in 1996 on most autos and light trucks sold in America, significant changes and improvements were built into the new on-board diagnostic system. One very important change was the addition of a second O2 sensor. This second sensor was located in the exhaust pipe at the outlet of the catalytic converter. V-6 and V-8 engines with true-dual exhaust will have two of each. The additional O2 sensor/s enabled the PCM to closely and accurately monitor the condition and efficiency of the catalytic converter. A P0420 (bank one), or a P0430 (bank two) code will be set if the PCM sees the trailing O2 sensor indicating a rich mixture similar to the front sensor for a given length of time.

A brief glossary of a few key OBD system component terms will make the following sections easier to understand.

AIR: Also referred to as Secondary Air System (or SAS), used to enhance cat converter efficiency.

ECT: Engine Coolant (sensor) Temperature. Sometimes known as CTS: Coolant Temperature Sensor.

MAP: Manifold Absolute Pressure. This refers to the pressure (vacuum) in the intake manifold.

BARO: Barometric (ambient) pressure sensor, used to set a baseline pressure to calibrate the MAP.

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MAF: Mass Air Flow meter. Not found on all vehicles, the MAF meter is a real-time real-volume meter, which reports actual airflow through the engine. A MAF equipped vehicle can compensate for increases or decreases in intake air flow and exhaust flow and adjust fuel trim accordingly. A MAP-only system cannot do this. The fuel delivery in a MAP-only system is programmed into the PCM by the OEM engineers. This system can only adjust to expected conditions within the factory-programmed values.

TPS: Throttle Position Sensor. Note: The new “throttle-by-wire” systems use two sensors, comparing one against the other.

VSS: Vehicle Speed Sensor.

HO2S: Heated Oxygen Sensor. We’ll just call them O2 sensors. All of them are heated these days.

CKP: Crankshaft position sensor, used to report RPM, monitor ignition timing and misfire.

CPS: Camshaft Position Sensor, used to identify cylinder #1.

EGR: Exhaust Gas Recirculation.

KNS: Knock Sensor, used to retard timing to eliminate pre-ignition and spark knock.

PID: Parameter Identification – aka Datastream Before we address a few specific repair strategies, let’s look at an overview of what the OBD system is doing during three different trips. The first trip we’ll look at will have the vehicle fully warmed up, and driving at a steady cruise of around 55 or so mph.

Steady cruise: The engine is at operating temperature, so the OBD system is in closed-loop. The PCM is relying on inputs from the MAP, TPS, ECT, and CNK, and CPS. The TPS shows only slight variations as the driver (or cruise control) adjusts power to maintain the desired cruise speed. When the driver adds a little power to climb a slight grade or to increase cruise speed slightly, the PCM sees a drop in vacuum (MAP) and a slight rise in TPS voltage. The PCM commands an increase in injector pulse width and retards the timing. This latter adjustment increases dwell time, improving fuel burn. If the vehicle is equipped with a MAF sensor, the MAP is referenced primarily to verify MAF and TPS signals.

When the demand for more power is satisfied, the PCM reverses everything it did above. The injector pulse width narrows and the timing advances. These actions return the vehicle to cruise/fuel mileage mode.

The O2 sensors are looking at all this activity, and are sending data to the PCM continually. The lead O2 sensor(s) (sensor 1) sends a varying voltage to the PCM several times a second. When the oxygen content of the exhaust stream is rich (low O2 content), the voltage signal sent to the PCM can be close to 1 volt. The full rich signal is actually about 800 mV to 900 mV. When the PCM sees such a signal, it will then narrow the pulse width to full lean, driving the O2 sensor to about 100mV to 200 mV. The length of time the pulse width is held wide or narrow determines the actual fuel delivery. Take note that an O2 sensor should cross between rich and lean at least 7 times a second on OBDII systems at 2500 rpm or greater. O2 sensors will get tired over time and the “cross counts” will fall to a level that hinders efficiency. If you are working on a high-mileage engine with the original O2 sensor(s), it may be money well spent if your customer will authorize you to replace them. Even with no codes in the PCM, fresh O2’s can produce a noticeable improvement in performance, mileage, and emissions.

In OBD II, the trailing O2 sensor (sensor 2) is in place to send a signal to the PCM, which should show a much lower content of fuel (high O2) than sensor 1 is reporting. The voltage swings for O2/2 should be between 430mV and 470mV. However, if the exhaust coming out of the cat closely resembles the

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exhaust going in for three consecutive trips, the PCM will store a P0420 (bank one) and/or P0430 code (bank two), and illuminate the MIL. The full rich to full lean cycle may seem to be a rather primitive strategy to handle fuel delivery (called “fuel trim”). However, the catalytic converter has to have it this way. The catalytic converter is designed to oxidize HC and CO into H2O and CO2, and reduce NOx to CO2, H2O, and N2. When the O2 sensor approaches a rich condition the PCM will command a lean injector pulse width, causing combustion to release the unused O2. The catalytic converter will store this O2 in its ceramic substrate.

As the O2 sensor approaches a lean condition, the PCM will command a rich injector pulse width, producing CO. This causes the catalyst temperature to rise dramatically, causing the NOx, CO, and HC to vaporize, separating into individual elements of C, H, N, and O. As this occurs, the O2 in the ceramic substrate will oxidize with the C element to form CO2, and a single O element will oxidize with two H elements to become H2O. The N element will then attach with another N to form N2.

At steady cruise, the PCM will command the EGR to crack open just a bit. The EGR gas is rich in HC, allowing the PCM to reduce pulse width and alter the ignition timing. The EGR gas causes the HC to oxidize, lowering combustion temperature, much like adding luke-warm water to boiling water until the boiling stops. With these results there will be an improvement in emissions and highway fuel mileage.

For a more detailed treatment of the exhaust stream and how you can use it to diagnose driveablilty issues, please see “5 Gas Diagnostics”, by Steve Zack, available at www.genisysotc/training.

Acceleration: What happens when the driver wants to accelerate? The PCM strategy calls this “acceleration enrichment mode”. On many V8 and high performance V6 engines, the PCM keeps the O2 sensors in closed loop, even during moderately heavy throttle opening. But many engines will briefly revert to open loop during acceleration, especially WOT. Here’s how acceleration enrichment mode works in those engines: During hard acceleration, the PCM relies on voltage data, first from the TPS, then from the MAF (if equipped), MAP, and CKS/CPS. When the driver drops the hammer, TPS will peg at about 4.3v to 4.7v.

The MAP voltage signal will increase (vacuum decrease), and MAF frequency will increase because of the increased air volume. Engine RPM aids the PCM in knowing just how much additional fuel the engine needs to meet the drivers’ power demands. The injector pulse width will increase to keep the air-fuel ratio correct for maximum acceleration. The timing will be retarded and dwell will increase. The increased dwell will provide additional voltage available at the coil to allow a longer oxidation process needed by the spark plug. This process also lessens spark knock. The transmission controller will delay up-shift points to hold a lower gear allowing a higher engine speed for more power and vehicle speed. The shift feel will be firmer and quicker. The torque converter will disengage as necessary to allow more RPM, adding torque and horsepower.

The MAP sensor is a very sensitive device, and can even sense a slight change in vacuum between individual cylinders. Because of the MAP’s ability to do this, this sensor is a primary sensor in fuel control. The engineering program that accomplishes this is a seldom talked about PCM strategy called “Timing MAP”. Timing MAP uses vacuum variations between cylinders to adjust individual cylinders’ pulse width as well as control individual ignition timing, keeping the cylinders in relative balance.

During hard acceleration, a greater amount of fuel will be used. This sudden increase in fuel will cause an increase in unburned HC and CO. The increases are moderate, and the ignition timing is retarded to compensate. The bigger problem is an increase in NOx due to a sharp increase in combustion temperature. The EGR is used to control combustion temperatures that will cause the formation of NOx. The EGR flow is tightly controlled, so the small amount of EGR diluting the fresh air/fuel mixture will cause no reduction in engine performance.

Deceleration lean-out mode: In DLOM, open loop, the PCM utilizes the TPS, MAP and CKP sensors to maintain proper fuel trim. As the driver begins to slow the vehicle, the first input to the PCM, just as in

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acceleration mode, is the TPS. The TPS tells the PCM that the throttle is closed to slow the vehicle.

Injector pulse width is decreased and timing is advanced. As air volume decreases, the engine vacuum will rise. MAP sensor voltage will begin to drop, and the PCM continues to command a leaner air fuel mixture. As the vacuum begins to stabilize, the MAP sensor will report that the vacuum level has returned to normal. At this point, the fuel trim reverts to Closed Loop, returning fuel trim settings to the O2 sensors.

As mentioned before, OBD II control strategies differ primarily from OBD I by the constant testing and evaluation of the emissions related parameters, sensors, switches, and actuators, and the electrical circuits that serves them. This testing is done by a series of Monitors. All this testing and evaluating is done to ensure the vehicle is performing to the minimum emissions standards set forth by the EPA. To trigger emissions DTC and set the MIL, the component or system must exceed 1.5 times the standard.

The government certification test is known as FTP, or Federal Test Procedure. This is an approximately 7 minute version of the 4 minute IM (Inspection and Maintenance) test.

The emissions Monitors operate much like a Ford KOER self-test. The difference is that the Monitor testing is performed during a normal driving period with speeds and times similar to the Federal IM240 inspection routine. (IM means “inspection-maintenance”) The IM240 Emissions Test satisfies the EPA standards for emissions system performance. This test procedure consists of a 7-part drive cycle, all done with the drive wheels secured between the two rollers of a chassis dynamometer and a tailpipe probe feeding a gas analyzer.

Before the testing is started, the engine is warmed up at least 40 deg. F, reaching 160 deg. F. This step puts the vehicle in closed loop. A Monitor watches for this and will only let the testing begin after these steps are done successfully.

A drive cycle occurs over a period of time, with varying speeds and loads. A Trip is a completion from start up to shut down. All Monitors must be run, or the trip is invalid. A “similar trip” is a second trip taken immediately after the first trip. The RPM must be within 375 of the previous trip, and the load must not vary more than 20% of all previous conditions. This “similar trip” is required for any Monitor that requires two or three trip cycles to set two or three flags which will illuminate the MIL. In addition, before the test can begin, the following must be in good operating condition: RPM, ECT, BMAP, and IAT. The Monitors will not run until the vehicle is in Closed Loop mode. The effected Monitor will run if the MIL is on. In addition, the Monitors will not run if the TPS or MAP is fluctuating, indicating varying speed and load. The Acceleration Enrichment or the Deceleration modes cannot be operating.

For the first part of the test, Part A, the vehicle idles for exactly 2.5 minutes, with the A/C and rear defroster turned on. During this time, the O2 sensor heaters, the AIR system (if equipped), Misfire, and the EVAP purge Monitors are run. In Part B, the vehicle accelerates to 55 mph at ½ throttle. Here, the misfire, fuel systems, and purge Monitors are run. In Part C the vehicle runs at a steady 35 mph for 3 minutes where the HO2S, EGR, purge, Fuel Trim, and AIR monitors are run. In Part D, the vehicle decelerates from 55 to 20 mph where the EGR, Fuel Trim, and purge Monitors are run. In Part E, the vehicle accelerates to 55 to 60 mph at ¾ throttle. Here the misfire, Fuel Trim, and purge Monitors are run. In Part F, the vehicle operates at a steady 55 to 60 mph for approximately 5 minutes. The catalyst, misfire, HO2S, EGR, purge, and fuel trim monitors are run. In Part G, the vehicle decelerates, ending the test drive cycle while running the purge and EGR monitors. If all Monitors run successfully, the vehicle will pass its emissions testing, and all Monitors will indicate “ready”.

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For OBDII testing, no tailpipe emissions are directly tested. All the information gathered by the test is communicated to the IM machine and the State government by the PCM through the OBDII port under the dash. No dyno is needed for OBD II testing, and the results cannot be successfully tampered with.

More on Monitors and how they work Continuous Monitors Misfire Monitor: This Monitor can pick up a misfire in the engine and set one of two codes. A P0300 is a “random misfire” (multiple cylinders). A P03?? is a specific-cylinder id. The Monitor cannot provide the reason for the misfire, e.g. ignition, fuel, or mechanical. The CKP, using an algorithm programmed into the PCM, detects the tiny slowing of the crankshaft when incomplete combustion takes place in the affected cylinder/s. After a sample of from 200 to 1,000 crankshaft revolutions (depending on OEM strategy), if the problem persists, the MIL is turned on.

Note: There are actually three separate Misfire Monitors, Types One, Two, and Three. The differences in the three are as follows: The OEM’s and SAE assigned misfire types one and three as “two-trip” misfire monitors. This two-trip strategy acts exactly like all two-trip events. That is, on the first misfire detected by the PCM, the misfire will be recorded as a Pending Code, with no MIL. If the second-trip misfire is detected, the MIL will come on, and the code will be stored as active.

A Type Two misfire indicates a much more severe misfire problem. As such, the MIL will be commanded on during misfire trip one. The one-trip MIL will be either steady or flashing. If the MIL is flashing, the catalytic converter is in imminent danger of severe damage. Diagnose and repair the cause of a flashing MIL immediately. It can happen that a flashing MIL can revert to a steady presentation. If this happens, there is no longer an immediate danger to the cat. However, the severe problem can suddenly reoccur, so do not let the vehicle out of the shop without repairing the misfire problem first.

Fuel System Monitor: This Monitor verifies that the O2 sensor cross-counts are quick enough, at least 7 times per second at 2,500 rpm or more. This applies in both short-term and long-term fuel trim modes.

This Monitor requires two consecutive similar trips to set the MIL Comprehensive Component Monitor (CCM): This Monitor scans for open or short circuits and electrical parameters that are out of range. This Monitor is either a one or two trip MIL, depending on the component.

Non-Continuous Monitors HO2S Monitor: Closed loop will occur only when the exhaust stream reaches 600-650 degrees. When closed loop occurs, this Monitor forces the fuel trim to “full rich” and watches for a voltage response of

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at least 600mV. The Monitor then forces the mixture to “full lean”, and watches for the voltage to go below 300mV. If the voltages are inadequate, or the cross-counts are too slow, an MIL will be set. This Monitor requires two similar trips to set the MIL. Catalyst Monitor: This Monitor will only run when the vehicle is running at a cruise speed for a minimum of 3 to 6 minutes. The Monitor watches the cross rates of HO2S 1 compared to HO2S 2. The downstream O2 must not cross more that 30% of the upstream O2. Mostly, HO2S 2 will stay in the “lean” range, reflecting a catalyst that is burning the residual HC and CO out of the exhaust stream. This Monitor requires three similar trips to set an MIL if a problem exists.

EGR Monitor: Steady cruise or deceleration is required to run this Monitor. When the PCM commands the EGR to open, total intake manifold volume will be increased. The MAP watches for a vacuum drop when this happens. If this vac drop is not detected by the MAP, a MIL will be commanded after two similar trips.

Readiness Status Readiness Status is a test that reviews the condition of the Monitors. If the Readiness Status records a Monitor that did not run because of an active or pending code, that Monitor will show “not ready”. When the condition that caused the failure is corrected, and the vehicle is driven in accordance with the applicable Drive Cycle, the Monitor will then run its test, and show the message, “ready”.

The State OBDII IM programs require all Readiness Monitors to run successfully before a vehicle can pass the IM test. However, some states will allow two Monitors to read “not ready” on 1999 and older vehicles and one “not ready” on 2000 and newer vehicles, as long as the MIL is not on. Check your State regulations for details. If the MIL is illuminated, the vehicle will not pass.

Freeze Frame This is a “snapshot” of one frame of data for several vehicle parameters that existed when the MIL was triggered. The PCM is required to record the following items: Loop Status, Calculated Load (expressed as a percent of 100), ECT, Short and Long Fuel Trim, MAP, RPM, and VSS. Some vehicle manufacturers add a few items to this recording such as TPS, IAT, and MAF. Note: The Freeze Frame is set the instant the MIL is illuminated. Keep in mind that the PCM always delays setting the MIL until it is satisfied the problem is persistent (this is known as Enable Criteria).

This may take several seconds to several minutes for the Enable Criteria to set the MIL. Therefore, the Freeze Frame may reflect conditions that may no longer be current.

Mode Six Mode 6 is a very sophisticated function that displays, along with min/max specs, the test results of each emission Monitor. Mode 6 information is the actual test result of the individual drive-cycle readiness tests of both continuous and non-continuous monitors.

During each drive cycle, the PCM will monitor and evaluate the Mode 6 test results and store them in the KAM (keep alive memory). The PCM uses a value called the “Exponentially Weighted Moving Average” or EWMA, to judge whether the test result is within the acceptable parameters. As the Monitor data is gathered by the PCM, the EWMA value is applied to the test, causing the points of the data to become more important as the problem becomes closer to failing the test. This allows for the latest test results to be of greater value in determining pass or fail conditions.

Note: be sure to read your Mode 6 info before you switch the vehicle off. Many vehicles may reset Mode 6 at key-off.

Most aftermarket scan tools cannot read or display Mode 6 information at all. The OTC Pegisys and the Genisys do a remarkable job of displaying the “TID” (test i.d.) and the “CID” (component i.d.) test information. When the OEMs’ began the switch to CAN in 2003 they changed the name of Mode 6 “CID”

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to “MID” (Monitor ID). You will find Component Parameters on the Diagnostic Menu of the Pegisys and Genisys . Scroll to “Component Parameters (mode 6)”, and press “enter”. Then scroll down through all the Monitors.

Many of the Mode 6 data PIDS are only given a number and not identified in plain English. The OEM’s assign these TID and CID numbers to suit them and do not readily give out this information. And there is no standard for what a TID or CID number refers to. OTC is identifying and adding English explanations to these numbers as quickly as we can learn them. The website “iatn.net” is a wealth of Mode 6 information, especially for Ford and Toyota. IATN.net is available to anyone with a computer.

To cloud the issue further, the actual test result numbers may be given not in the familiar decimal system, but in a scientific number system called “hexadecimal”. Hexadecimal values are reported with a combination of numbers and letters, and are identified as Hexadecimal with a dollar symbol ($) prefix.

If you have identified what TID and CID you are dealing with, your standard Windows computer has a calculator that will convert Hexadecimal to decimal. To do this translation, click All Programs, and then click on Accessories. Next, select Calculator, and then click on View and select “Scientific”. Next, click on “Hex”. Then enter the Hexadecimal value (let’s use 33E as an example) in the value box. Then select the “Dec” button. Voila! 33E becomes 830! Compare 830 to the min/max limit in the Mode 6 test to determine the health of the Monitor results.

Incidentally, GM has a DTC function called “Failure Records”, for OBD II vehicles. This info is essentially the same as Mode 6, and is easily read and understood.

The information given in Failure Records, as well as in Mode 6, can be used to predict if a system is about to store a two trip failure before the MIL is set. This info can be used as repair verification, saving you a lot of time or even a comeback.

In Part Two of this series, we will delve into several repair strategies on the three domestic vehicle makes. Of course, our examples will also apply to most OBDII vehicles, domestic and otherwise. These examples are all based on real-world, common-failure events that you should find familiar, and we hope our repair ideas will be helpful. Stay tuned…

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Trouble Shooter Deciding to replace an expensive emissions control component requires confidence in the accuracy of your diagnosis. Is the decision tougher or easier when you’re working on your own car?

Ready to Buy a Cat?

Karl Seyfert

Freeze frame data: Pusheng Chen

kseyfert@motor.com

and listening for a sound change). I was unable to find any leaks. The BARO reading of 98KPa seems to be in agreement with where I live (Metro Detroit area).

I am trying to rule out other possible explanations for the P0420 before having the faith to replace the cat. What puzzles me is why bank 1 is in open loop while bank 2 is in closed loop when P0420 is set.

I searched for the most common OBD II codes on an automotive reference website. P0420 was at top of the list (with 13.2% of the total). P0430 was number 10 with 3.2% of the total. I can’t think of a reason why there are significantly more P0420s than P0430s recorded. I think this is interesting.

I typically try to spend enough time on a diagnosis until I am confident about making a recommendation to replace any parts. But this P0420 with bank 1 in open loop puzzles me. I have included the freeze frame data that was stored at the same time the DTC was set. I would appreciate your help.

Pusheng Chen Novi, MI

I am having a problem with a DTC P0420 that’s puzzling me. The vehicle is my 2009 Cadillac STS, which has about 85,000 miles on it. It’s equipped with a 3.6L direct fuel injection V6 engine, a sixspeed automatic transmission and AWD. The freeze frame data indicates bank 1 was in open loop when the P0420 was set. Bank 2 was in closed loop. I cleared the code and it came back in about 300 miles. Once again, bank 1 was in open loop when the DTC set. During subsequent testing, both bank 1 and bank 2 went into closed loop within a few minutes after engine starts.

The B1S1 oxygen sensor switches normally, and responds to throttle (wide-open and closed).

Even though it appeared to be functioning normally, I replaced the B1S1 O2 sensor with an OE part anyway, thinking it might be an intermittent O2 sensor. After that, I cleared the code, but it came back again in about 700 miles.

I checked for intake leaks (with propane) and exhaust leaks (by plugging the tailpipe with a rag

Freeze frame data is perhaps the most useful information available when attempting to determine the cause an OBD II diagnostic trouble code. This data is collected at the moment the DTC is set and is the next best thing to being there when it happens. What can the data shown here tell us about the P0420 that was set on the 2009 Cadillac STS when it was collected?

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Any DTC that sets only every 300 to 700 miles is going to be tough to diagnose. And one that points to possible replacement of an expensive emissions control component like a catalytic converter when it does is going to be even tougher. So first let me applaud your dedication. And second, thank you for the foresight to save and include the freeze frame data with your note. This data may not provide all of the information we need to reach a diagnostic conclusion, but it should help to get us pointed in the right direction.

P0420 is a very popular DTC—or unpopular, depending on how you look at it. It indicates that the PCM has determined that the catalytic converter is performing below an established threshold. OBD II’s number one mission is to keep vehicle emissions as low as possible, and it can’t do that without a properly functioning catalytic converter (or converters, in some cases).

OBD II keeps a close eye on converter perform-

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Trouble Shooter ance, and when performance drops below a prescribed level, the PCM will set a DTC. Some might argue that performance levels are set too tightly, making it all too easy for a converter to fail an OBD II monitor.

Many vehicles are equipped with 4cylinder engines, which typically have just a single catalytic converter, or one large and one small cat, coupled with a set of pre- and postconverter oxygen sensors situated at either end of the main cat. Your STS is equipped with two of everything because it’s a V6 with separate emissions equipment for each bank. P0430 points to a bank 2 catalytic converter that’s operating below an established threshold. Many vehicles don’t have this second converter, which I believe explains why P0430 is so much further down on the “hit parade” of DTCs, when compared to the charttopping P0420. If all vehicles had two of everything, the two catalyst efficiency DTCs would probably be more evenly ranked in terms of occurrence.

The PCM doesn’t have a five-gas exhaust analyzer probe stuck up the tailpipe of your STS, so how does it make the determination that the converter is functioning below the performance threshold? The PCM runs a catalyst monitor test only when certain driving conditions have been met. The engine and converter must be at operating temperature, and the engine may be idling or running under light load at low speed. Your freeze frame data indicates the STS’s engine speed was 1228 rpm.

The fuel system should also be in closed-loop fuel control (this is key).

There must not be any other unfulfilled criteria or previously stored DTCs that would keep the catalyst efficiency monitor from running.

Once the PCM has determined that all preconditions have been met, it temporarily forces the air/fuel mixture rich, to deplete any stored oxygen in the converter. Then the PCM temporarily forces the air/fuel mixture lean to determine how long it takes for the converter to react and for the downstream oxygen sensor to change its switching activity. If the converter takes too long to resume functioning (indicated by postconverter oxygen sensor activity), it means the cat-

alyst is not working efficiently enough to maintain the vehicle’s emissions levels within prescribed limits. OBD II will then fail the converter, set a DTC P0420 and turn on the Check Engine light.

I believe your vehicle is setting a DTC P0420 only every 300 to 700 miles because that’s how long it takes for all of the preconditions to be met, and for the PCM to run the catalyst efficiency monitor. Alternately, the monitor may be running more frequently, and failing only once every 300 to 700 miles.

The key piece of information contained in the freeze frame data is the indication that bank 1 was in open loop at the time the freeze frame data was stored. On the face of it, this makes no sense, as the catalyst efficiency monitor should never have run in the first place with half of the fuel system still in open loop. Achieving closed loop is one of the first preconditions the fuel system would have to satisfy before the PCM would even consider running the catalyst efficiency monitor.

We know that freeze frame data is stored at the moment the PCM decides to flag a DTC. So in this case the data was probably collected a certain period of time after the PCM attempted to run the catalyst efficiency monitor. The fuel system had to be in closed loop when the monitor began to run, but something happened after that, and it was no longer in closed loop when the freeze frame data was stored. This is a hypothesis, as we don’t know how quickly the PCM updates the freeze frame data we’re now using for our diagnosis.

I’d suggest you look for a component that’s capable of intermittently kicking the fuel system out of closed loop. This may be happening at other times, besides when the PCM is attempting to run the catalyst efficiency monitor. Besides the pre- and postcatalyst oxygen sensors, most of the other input sensors have their own OBD II DTCs that should give you an indication of a problem. But it may be too intermittent to trigger a DTC and the only way you may be able to identify it is by monitoring a limited set of PIDs, waiting for the glitch to reveal itself. It can’t hide forever, and you’ve already shown that you have the patience to wait.

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DATASTREAM

Photoillustration: Harold Perry; photos: Wieck Media & Jupiter Images

IN-DEPTH ANALYSIS

BY SAM BELL We began this two-part article with a discussion of preliminary OBD II datastream analysis, conducted with the engine off.

We’re going deeper this time, to explain the value of datastream information collected with the engine running.

L

ast month’s installment on datastream analysis focused on the value of freeze frame data, Mode 5 and Mode 6 data and KOEO (key on, engine off) datastream. This month’s discussion picks up where we left off, with KOER (key on, engine running) analysis. So go ahead, start the engine!

I recommend that KOER data collection always start in the generic, or global OBD II interface. Why? Because generic datastream PID values are never substitutes for actual sensor readings.

For example, you can disconnect the MAP sensor connector on a Chrysler

product and drive it around while monitoring datastream in the enhanced (manufacturer-specific) interface. (Try this yourself; don’t just take my word for it.) You’ll see the MAP PID change along with the TPS sensor reading and rpm, showing a range of values that reflect likely MAP readings for each condition, moment by moment. These are substituted values. If you looked at the MAP voltage PID, however, it would show an unchanging reference voltage.

In the enhanced interface, substitutions can and do occur. But in the generic interface, substituted values are never allowed. You would see MAP shown at a constant pressure equal to something a

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Chart & screen capture: Sam Bell

DATASTREAM IN-DEPTH ANALYSIS

Data collection and analysis might yield some helpful information, if you can find the wheat within the chaff. This is only a small portion of a larger data set with 100 values per PID.

bit higher than BARO. The generic interface allows calculated values, but never substituted values.

So, what are we looking for, now that we’ve finally started the engine? The specific answer, of course, will depend largely on the details of the customer complaint and/or DTC(s) that are stored. We might, for example, be focusing on fuel trim numbers (and trends) if our code suggests an underlying air/fuel metering problem. We might be looking most closely at engine coolant temperature, and time-until-warm measurements when that seems warranted. Perhaps our problem lies in the evap area, or involves EGR flow. But ultimately, it doesn’t matter what the specific issue is; we’ll have to focus in on the systemic interactions that determine the overall characteristics of a particular data set.

Here’s a concrete example to illustrate what I mean. The vehicle in question is a 1999 Chevy Venture minivan with the 3.4L V6. There was a DTC

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P0171 (Exhaust Too Lean, Bank 1) in memory with an active MIL. The sum of Short Term and Long Term Fuel Trims in freeze frame was in excess of

When evaluating a fuel trim trouble code, one of the first steps must always be to verify that the oxygen sensor (on which the DTC is based) is functioning correctly.

50%. Fuel pressure and volume had been verified as within specification.

When evaluating a fuel trim trouble code, one of the first steps must always be to verify that the oxygen sensor (on which the DTC is based) is functioning correctly. During the test drive, I observed the O2 sensor switching rich, but not as often as would be expected if the very large fuel trim corrections shown were actually effective. Indeed, on the face of it, datastream seemed to confirm the DTC. Longtime readers, however, can probably anticipate what my next tests were: I checked the actual lambda value of the exhaust gases. Then I looked for a dynamic response as I artificially enriched the system with a blast of propane, then enleaned it by disconnecting a major vacuum hose. (See “What Goes In…Harnessing Lambda as a Diagnostic Tool” in the September 2005 issue of MOTOR. Search the index at www.motormagazine.com for all MOTOR magazine articles mentioned.) Hav-

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Graphical representations of scan data “movies” can speed analysis. As an added bonus, using your scanner’s flight recorder mode allows you to concentrate on your driving. The data set here clearly points to a lack of adequate fuel volume. This graphical representation is derived from the exact same movie capture seen in the chart on the previous page.

ing found the idle lambda at a ridiculously low value of .85 (indicating a mixture with 15% more fuel than needed), I was not surprised to see that the O2 sensor didn’t register a rich condition until the engine was very nearly flooded with propane. When I removed the purge hose, engine rpm climbed and the engine smoothed out, while lambda marched toward the stoichiometric ideal value of 1.00. Once the faulty O2 sensor was replaced, all aspects of driveability improved, and the minivan returned to its previous fuel consumption levels.

Dynamic tests verify DTC accuracy.

In some instances, we may be able to utilize bidirectional controls embedded within our scan tool packages to actuate various components. In other cases, we may need to improvise, using signal simulators, power probes, jumpers, propane or just good, old-fashioned test driving as required to initiate change within the system we’re working on.

(I’m not saying that it will always be as

easy as it was with the Venture. You and I know there will be problems that don’t set DTCs, problems that do set DTCs that have no apparent connection to the

One of the most powerful features of most scan tools— the so-called flight recorder—seems to be one of the least used. But it’s an analytical tool of considerable value.

actual root fault and, of course, problems that set appropriate codes yet are still really hard to diagnose.)

Floodlights and Spotlights One of the most powerful features of most scan tools is, as nearly as I can tell, one of the least used. This is the so-called flight recorder, data logger or movie mode. By whatever name it’s known, this is an analytical tool of considerable value.

Take a look at the portion of saved scan data portrayed in the chart on page 38. As you see, any value in that information is well hidden. This might be termed a “floodlight” view, showing too many values for too many parameters.

But look at the “spotlight” view above, where I’ve selected and graphed a few of the same PID values. This was a vehicle where there was no DTC stored in memory. By including both upstream O2 sensors, I have provided myself a cross-check, as there is less likelihood of

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DATASTREAM IN-DEPTH ANALYSIS both being bad. Similarly, MAF and rpm track nicely with one another, again providing a good cross-check. The data values at the cursor (the vertical line at frame 2) are called out at the left side of each PID’s plot. The upstream O2 sensors are switching nicely at 2000 rpm (as shown at frame ⫺51), but the graphic interface reveals an obvious problem at

higher speeds as the O2 sensors flat-line lean. A new fuel pump restored the missing performance.

Slow Motion and High Speed Moviemakers speed up or slow down the action on the screen by shooting at different numbers of frames per sec-

ond. When film shot at 20 frames per second is played back at 60 frames per second, the action seems to be occurring at three times the speed. Just as a 56k dial-up modem is slower than a DSL Internet connection, scan data transfer rates also vary according to the interface used. Generic communication modes often travel at a crawl, es-

Monitors 1.01

M

ost MOTOR readers have at least a passing familiarity with the concept of OBD II monitor completion status. Even so, a brief refresher may be in order. OBD II monitors are simply formalized sets of self-tests all related to a particular system or component.

Continuous monitors. With a few very rare exceptions (mostly for 1998 and earlier models), the so-called continuous monitors always show up as “complete,” “done” or “ready.” Take this status report with a grain of salt. Unplug the IAT sensor, start the engine and check that the “Comprehensive Component Monitor” readiness status shows complete. Is the MIL on? Are there any pending codes?

How long would you have to let the vehicle idle before it will trip the MIL and show a P0113 (IAT Sensor Circuit Voltage High) DTC? As it turns out, depending on the specific make, model and powertrain package, there are several specific criteria that must be met before the code will set. In one instance, the PCM must detect a VSS signal of 35 mph or more and an ECT value of 140°F or more, the calculated IAT must be less than ⫺38°F and all of these conditions must be met for at least 180 seconds of continuous duration, during which no other engine DTCs are set—all while MAF is less than 12 grams per second. (This particular example, incidentally, is a two-trip code. Some other manufacturers may make this and other DTCs under the component monitor’s jurisdiction into one- or twotrip codes, sometimes with even more complicated entry criteria.)

Continuous monitors include the comprehensive component monitor, the fuel monitor and the misfire monitor. Each monitor runs continuously when conditions are appropriate, but not during all actual driving. For example, the misfire monitor is often suspended during 4WD operation, since feedback through the axles over rough roads might cause uneven disruption of the CKP signals, which could

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otherwise be misidentified as misfires. Similarly, extremely low fuel tank levels may suspend both misfire and fuel system monitors to avoid setting a DTC for running out of gas.

Noncontinuous monitors. As I pointed out last month, it’s important to note the readiness status of the other, noncontinuous monitors as well. These are the monitors whose status will change to “incomplete,” “not ready” or “not done” when the codes are cleared. If a vehicle arrives at your shop showing one or more incomplete monitors, it’s likely that someone has already cleared the codes before it got to you. (There are a few vehicles—for example, some 1996 Subarus—which may reset monitor status to incomplete at every key-off, or other vehicles which may have certain monitors which cannot be made to run to completion in normal driving, such as the evap monitor on some Toyota Paseos.) If a vehicle shows up with incomplete monitors, however, you should certainly document that fact on your work order and be sure to advise the customer that there’s a very real possibility that one or more other codes may recur after the current repair has been completed. For more on this subject, see my article “How Not to Get MILStoned” in the April 2004 issue of MOTOR. More importantly, for our present purposes, the existence of incomplete monitors means that you may not be getting the whole picture as to what ails the vehicle you’re looking at. Keep an open mind, remembering that there may be other, as yet unknown issues hidden behind that incomplete monitor, and try not to rush your diagnosis. As mentioned in last month’s installment, there may be some valuable data accessible via Mode 6 even if the monitor is not complete, but there is a very real possibility that Mode 6 data for any incomplete monitor may turn out to be unreliable. And, of course, don’t overlook any pending DTCs. Remember, these do not illuminate the MIL, so you must seek them out on your own.

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DATASTREAM IN-DEPTH ANALYSIS pecially in comparison to CAN speeds.

If you’re stuck with a generic interface, you can often accomplish more by looking at less.

The key here is PID selection.

Choose the smallest number of PIDs that will give you the information you

actually need. Three or four are usually sufficient. This is your version of the filmmaker’s high-speed action trick, as you get more updates per unit time the fewer PIDs you select.

With several hundred possible PIDs from which to choose, it’s just too

Lights Out?

I

t seems like a no-brainer: When you’re done with all your diagnostic tests and you’ve made the necessary repairs, you should turn off the MIL, right? That’s what your customer probably expects, and as we all know, meeting customer expectations is an important part of running a successful business.

But there are often times when you should leave the MIL on. If your area uses an OBD II “plug & play” emissions test, the regulations usually require that no more than one monitor can be incomplete as of the time of testing for model year 2001 and newer vehicles, with no more than two incomplete monitors for 1996 to 2000 models. In some areas, retest eligibility requires that the converter monitor must show “complete” before a retest is valid.

If an emissions test or retest is looming in your customer’s future, you and he must work out the pros and cons of clearing the codes and resetting the monitors to “incomplete.” If you clear the codes, the monitors will reset as well. This will require that someone will have to drive a sufficient number of monitors to completion before a retest will be valid. If local weather conditions, for example, will prevent the monitors from running in a timely way, your customer might be better off if you leave the MIL on. Then your customer would have to drive only those portions of the drive trace needed to run the monitor under which the current DTC set.

For example, if you’re in the frigid climes of an upper Midwestern winter and a customer’s vehicle failed an emissions test because of a faulty O2 sensor heater, you’ll both be ahead if you don’t clear the code, letting it expire naturally as the heater monitor runs successfully to completion on the next two trips. This will avoid the necessity of rerunning all the rest of the monitors. Of course, if the vehicle failed the evap monitor, you’ll be better off clearing the code, because prolonged subfreezing temperatures may make running that particular monitor successfully virtually impossible for weeks at a time.

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easy to miss an intermittent data glitch, or to drown in a sea of too much information (see “Live Data vs.

‘Live Data’” on page 44).

Most MOTOR readers are familiar with the ways in which some of the major OEMs have organized data PIDs for display in their enhanced scan tool interfaces. Groupings such as Misfire, Driveability, Emissions, Accessories and the like are good examples of the types of data sets you may want to construct while analyzing different sorts of problems. Tracking down a nasty intermittent problem? Don’t hesitate to pare down the OEM groupings even further to speed data updates.

Code-Setting Criteria and Operating Conditions If we’re trying to resolve a MIL-on complaint, it’s critical that we first review both the exact code-setting criteria and the operating conditions as revealed in our previously recorded freeze frame data. We’ll need to drive in such a way as to complete a good “trip” so the affected monitors can run to completion. (For a more detailed discussion of OBD II trips and monitors, see “Monitors 1.01” on page 40.) If we fail to meet the conditions under which the self-test (monitor) will run, we cannot hope to make progress. Using the previously recorded freeze frame parameters gives us a good general idea of the operating conditions required. Merely duplicating speed, load, temperature and other basic characteristics may not be enough. This is why we need to review and understand the details of the code-setting criteria and the monitor’s self-test strategy. For example, some monitors cannot run until others have already reached completion. A typical example would be a catalytic converter monitor that is suspended until the oxygen sensor monitors have run and passed.

Some trouble codes, or even pending codes, suspend multiple monitors. Other vehicle faults may then go undetected until all monitors can run again. A P0500 (VSS Malfunction) in a Corolla, for example, will effectively suspend even the misfire monitor.

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DATASTREAM ANALYSIS The net result is that we may have to clear the current DTCs and extinguish the MIL before our test drive can bear fruit. (But again, please be sure to read and record all the freeze frame data, the status of all monitors, the list of both current and pending DTCs and any available Mode 6 data before clearing the MIL (see “Lights Out?” on page 42).

We’ll need to drive long enough to let the monitors in question reach completion. In some cases, this may require an extended period of time. Many Ford products, for example, normally require a minimum of a six-hour cold-soak before the evap monitor can run, although there may be ways to force this issue in some instances. Many Chrysler oxygen sensor monitors run only after engine shut-down (with key off),

Live Data vs. ‘Live Data’

I

ntermittent interruptions of sensor data can cause tricky driveability problems.

Some glitches may set a DTC while others may not. While viewing datastream may reveal an intermittent sensor problem, it should not be relied upon to do so. The issue, once again, is in the data rate. Even a moderately fast interface, say the 41.6 kbps (kilobytes per second) J-1850 PWM used on many Ford products, can easily miss a several-millisecond dropout if it’s not that particular PID’s turn in the datastream. Where symptoms or DTCs point toward an intermittent sensor glitch, you’re probably better off breaking out your scope or graphing multimeter.

so that no amount of driving will ever bring them to completion. Certain monitors, and apparently even certain scan tools, may require a key-off sequence before the monitor status will update from incomplete to complete. MOTOR offers an excellent resource to help you understand these details—the OBD II Drive Cycle CD Version 7.0, available from your local MOTOR Distributor (1-800-4A-MOTOR).

In some cases, local weather conditions may make monitor completion seem impossible until a later date, usually because of ambient temperature requirements, although sometimes as a result of road conditions. In most cases, however, it will still be possible to complete the monitor by running the vehicle on a lift or dynamometer. This option may occasionally result in setting, say, an ABS code, but most monitors can be run to completion swiftly and successfully on a lift. This option may also offer a safer, faster alternative to actual driving, as trees and telephone poles are less likely to jump in front of a vehicle on a stationary lift.

Circle #22

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Conclusions Proper in-depth datastream analysis can often light the way toward correct diagnosis of driveability concerns.

Recording all available DTCs, pending DTCs, freeze frame data and Mode 5 and Mode 6 results before clearing any DTCs is essential. Specific setting criteria for each DTC are manufacturerdetermined, regardless of whether the code assigned is generic or manufacturer-specific. Freeze frame data sets can be used to recreate the operating conditions under which a previous failure occurred and can help illuminate the conditions under which certain self-tests are conducted. Mode 5 and Mode 6 test results can help in analyzing the type and extent of certain failures. KOEO datastream analysis can sometimes reveal sensor faults or rationality concerns that might otherwise be overlooked.

Looking at KOEO and KOER datastream on a regular basis makes knowngood values familiar. Once you know

the correct values, the conditions accompanying problems identified by freeze frame are easier to spot. KOER data can highlight current problems, es-

When trying to resolve a MIL-on complaint, it’s critical to first review the exact code-setting criteria and the operating conditions as revealed in the freeze frame data.

pecially when used in conjunction with graphical scanner interfaces. Generic data PIDs cannot include substituted values, and so may point up faults easily overlooked in more enhanced interfaces. Careful selection of customgrouped PIDs can provide faster scanner update rates.

Pick your tools wisely. To verify hard faults, monitor datastream as you run actuator tests. Look for any mismatch between the command sent to a component and its actual response. For intermittent problems, record and graph data. In tough cases, test circuits with your scope or meter to verify actual voltage for comparison to specs.

Used properly, these techniques will help you arrive quickly and confidently at an accurate diagnosis of the root cause of most driveability complaints.

This article can be found online at www.motormagazine.com.

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Trouble Shooter One definition of insanity is repeating the same action and expecting a different outcome. After multiple replacements of the same part, it may be saner to look elsewhere for the cause of the failure.

Déjà Vu All Over Again

Karl Seyfert

were the same (reduced power) and the same DTC P0121 was stored in memory. I followed all of the recommended diagnostic procedures, then replaced the throttle body (a second time).

We recently heard from the customer, and the vehicle is apparently experiencing the all-toofamiliar reduced power symptoms and the Check Engine light is on. Is it time to install a new OE part? I have not previously had any problem with reman parts purchased from this supplier. Is there an underlying issue that is shortening the throttle body’s life span? I don’t want to throw any more of the customer’s money at this problem without finding an answer.

Jerry Burns Trenton, NJ Due to the large amount of time that has elapsed between each failure occurrence, we’d have to consider this to be a very intermittent

Photo: Karl Seyfert

kseyfert@motor.com

A 2007 Chevy Impala with a 3.5L engine came into our shop for the first time about a year and a half ago. The MIL was on, the engine had reduced power and DTC P0121 (Throttle Position Sensor 1 Performance) was stored in the PCM memory. I removed, cleaned and remounted the throttle body, then flashed the PCM and inspected the wiring harness. The DTC did not return, so the vehicle was returned to the customer. About six months later, the throttle body failed with the same DTC P0121 stored. At this time the throttle body was replaced with a remanufactured aftermarket part. The wiring harness was also rerouted, as it did not appear to have enough slack between the body and the engine.

Fast-forward another six months or so and the throttle body failed again. The symptoms

Perhaps due to safety considerations, this 2007 Chevy Impala throttle-by-wire throttle housing has “no user serviceable parts inside.” Any accumulated gunk can be removed from the area around the throttle blade, but familiar adjustments to components like the TP sensor are no longer possible.

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Trouble Shooter

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problem. Intermittents are certainly more difficult, but not impossible, to diagnose.

Perhaps the most helpful information that could be used to solve this problem would be the freeze frame data. This would tell you the operating conditions at or near the moment when the DTC P0121 was stored. Were the freeze frame data parameters the same (or similar) each time the DTC was stored? If they were, is it because more than one throttle position sensor has failed in exactly the same way? This scenario is not impossible, but it seems statistically unlikely, unless a series of faulty parts were involved.

In general terms, what do we know about the possible causes of a P0121? It begins when the PCM detects a malfunction that’s causing an excessively low or high voltage signal to be sent from throttle position sensor to the PCM. This can be caused by a throttle position sensor that has an internal fault. Since the sensor can’t be replaced separately, this is probably why you’ve been installing replacement throttle body assemblies. The DTC can also be caused by a throttle position sensor harness that’s open or shorted. A poor or intermittent electrical connection in the throttle position sensor circuit could also be to blame. Lastly, and probably the least likely, the PCM may be experiencing intermittent failures.

Because this is a throttle-by-wire system, the PCM responds to problems with its inputs by reducing engine power. Under normal conditions, the PCM uses the TP sensor input to detect the actual position of the throttle valve, as well as the opening and closing speed of the throttle valve. If the TP sensor reports that the throttle valve is closed, the PCM would use this information to control other functions, such as fuel cut.

If the PCM does not have accurate information about how far open or closed the throttle valve may be at a given moment, it can’t accurately control the opening and closing of the throttle from that point on. The reduced engine power allows the driver to (barely) limp the car into a service facility. This may be an inconvenience,

but should be considered safer than the possibility of a runaway throttle.

When the customer brings the vehicle to your shop this time, make certain you capture the freeze frame data before making any changes to the PCM or its programming. When did the DTC store? What was happening at the time? With the original throttle housing still in place, make your best attempt to duplicate these conditions.

Monitor the relevant PIDs with your scan tool. To open an even larger window into this problem, attach a digital storage oscilloscope to the TP sensor’s data lines. Watch the scope for any indication of signal abnormalities as you work the throttle through its normal range of movements. This may be a temperature-related failure, so it may be necessary to drive the vehicle long enough to get everything under the hood good and warm.

There are a few harness connections between the TP sensor and the PCM. Examine each of them closely for any signs of looseness, fretting or other damage. You mentioned that the harness appeared too tight between the throttle housing and the body. Is it possible that this is or was causing a harness connector to partially separate, causing the TP sensor signal to weaken or intermittently drop out? Once again, manipulating the harness while observing the TP sensor signal on the scope may allow you to capture an intermittent failure.

Lastly, there’s your question about the quality of the parts involved, and the possible link to repeated failures. In my research, I found that throttle housing failures are not unheard of on these vehicles, so the original equipment parts certainly are not unbreakable.

Some techs have experienced problems with remanufactured replacement parts, while others have not. Before pointing the finger of blame at any replacement part, be it original equipment or aftermarket, new or remanufactured, I’d suggest you first make certain you’ve eliminated all of the other possible problem causes. Installing another throttle housing without doing so might buy you some time, but déjà vu could still be a possibility.

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Driveability Corner New PIDs provide additional information that can be included in your diagnostic efforts. But before it can be used, you must understand how it was obtained and what it’s intended to represent.

Mark Warren

PID—there is no differentiation for Bank1 and Bank2.

Now let’s get into the layout of the screen capture below, from the 2010 Tacoma: In the top chart, rpm is in red (the scale on the left-hand side) and vehicle speed is in green (the scale on the right-hand side).

In the second chart, air/fuel ratio sensors Bank1 and Bank2 are in milliamps, and both are scaled on the left-hand side.

In the third chart, the air/fuel ratio sensors Bank1 and Bank2 are in volts, and both are scaled on the left-hand side.

In the fourth chart. postcatalyst O 2 Sensors Bank1 and Bank2 are in volts, and both are scaled on the left-hand side.

In the last chart, the commanded EQ ratio is scaled on the left-hand side.

All data to the left of the dotted line in the screen capture is a baseline test drive ending with a long idle period prior to introducing a skew in B1S1 AFR sensor (the ver-

Screen capture & chart: Mark Warren

smwarren@motor.com

T

he commanded equivalence (EQ) ratio parameter (PID) is required in the generic datastream on all passenger vehicles since 2008 (see the EQ to air/fuel ratio [AFR] matrix on the next page and the SAE definition in the box on page 13). An EQ of 1 equals 14.7:1 AFR. This PID should reflect the commanded air/fuel ratio. That being said, there are no Bank1 and Bank2 EQ ratio PIDs, and can’t the EQ or AFR be different for each bank? Are the two averaged?

Yipes! How is this going to work on a vehicle?

This test was performed on a 2010 Toyota Tacoma with a 4.0L engine. It’s important to note that this may not be representative of other vehicles; this is one test. Also, this test is not intended to be critical of any implementation of the EQ PID. I think the problem is in the original definition of this

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tical dotted line). The solid green line is the point of measurement for the reading in the small boxes to the right of the parameter name on the chart. Finally, I’ve drawn a solid fine black line horizontally in the EQ chart to show EQ equals 1.

amount of amperage used and the conversion to volts scaling. Note the postcatalyst oxygen sensors also following each other reasonably close-

ly. It’s noteworthy that at 105,000 miles, the rear O2 sensors don’t go above .8V and lay flat on zero for some period of time. Perhaps these continued on page 13

Data Analysis Remember that the air/fuel ratio sensors (charts 2 and 3) read high when lean and low when rich—the opposite of the O2 sensors that are

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low when lean and high when rich.

The high (lean) spikes in the AFR sensor data reflect deceleration fuel-cut enleanment. Note the Bank1 and Bank2 AFR sensors following each other closely in the baseline data.

I put in the AFR milliamp and voltage data to demonstrate the tiny

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W W W M O H A W K L I F T S C O M

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Driveability Corner sensors are showing some age.

Note that the EQ PID in the baseline data period is pretty active when the truck is being driven.

Look at the EQ relative to the top

At 105,000 miles, the rear O2 sensors don’t go above .8V and lay flat on zero for some period of time. chart of rpm and mph to get an idea of the changing load. Notice that the fuel-cut events that are reflected well in the AFR, and O2 sensor

SAE Definition: Commanded EQ Ratio Fuel systems that utilize conventional oxygen sensors shall display the commanded open-loop equivalence ratio while the fuel control system is in open loop. EQ_RAT shall indicate 1.0 while in closed-loop fuel.

Fuel systems that utilize widerange/linear oxygen sensors shall display the commanded equivalence ratio in both open-loop and closedloop operation.

To obtain the actual A/F ratio being commanded, multiply the stoichiometric A/F ratio by the equivalence ratio. For example, for gasoline, stoichiometric is 14.64:1 ratio. If the fuel control system was commanding a .95 EQ_RAT, the commanded A/F ratio to the engine would be 14.64 x 0.95 = 13.9 A/F ratio.

data are not well represented in the EQ data. The EQ ratio data looks almost backwards when compared to the rich periods on the AFR’s (low) and the O 2 ’s (high). The EQ looks like it’s going in the opposite direction.

Okay, now let’s look at the point of defect. I skewed the B1S1 AFR sensor. You can see the immediate skew in the AFR sensor and O2 sensor data. The O2 sensor rails at the bottom (lean). The AFR B1S1 initially skews down, recovers at idle and then skews down again under load. The AFR sensor is skewed to look rich, a false signal I created.

The fuel response is to react to lean the “rich” mixture. The rear O2 sensor shows the enleanment and the EQ shows the command to lean.

Is the EQ using just Bank1? Is it an average of both banks? Right now I have more questions than answers. I’ll skew Bank2 next time and see where it leads.

IT’S NOT FOR EVERYBODY. IT’S FOR YOU.

WD-40 ® Specialist ®. A line of superiorperforming specialty products formulated for those who demand the best.

See what yyour our fellow pros think at WD40Specialist.com

February 2015

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Automotive Repair Library, Auto Parts, Accessories, Tools & Equipment, Manuals & Books, Car BLOG, Links, Index, CarleySoftware

OnBoard Diagnostic II (OBD II) HELP Real information you can use to diagnose your car or truck Copyright AA1Car.com

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The Malfunction Indicator Lamp (MIL) or CHECK ENGINE light as it is more commonly called, is essentially an emission warning light. If the light comes on, it means the Onboard Diagnostics II system (OBD II) has detected an emissionsrelated problem. OBD II is designed to turn on the MIL light if a problem occurs that may cause emissions to exceed federal limits by 150 percent. The problem has to occur more than once, and it must be significant enough to create a potential emissions problem (one serious enough to prevent a vehicle from passing an emissions test).

In the real world, the MIL lamp often comes on for what seems like trivia reasons (like a loose gas cap). But there's no way to know what's triggering the light until the vehicle is diagnosed. The problem may be something minor that has little or no effect on driveability, or it may be something more serious that is affecting engine performance.

The mysterious nature of the MIL lamp, which most people call the "Check Engine" light, terrifies and confuses a lot of motorists. Except for a few luxury vehicles that actually display a fault message when the MIL lamp comes on, most

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provide no information whatsoever other than something is wrong. The motorist has no way of knowing if the problem is major or minor -- or what it will ultimately cost to have the problem diagnosed and repaired.

Some motorists, on the other hand, seem unfazed by warming lights. As long as their vehicle continues to run, they see no urgency to have their engine checked, to slow down or to do anything out of the ordinary. Others are optimists and hope that if they keep on driving, the light will magically go out. Sometimes it does, much to their relief. But when the light refuses to go out, or it comes and goes like the ups and downs of the stock market, they panic and don't know what to do.

Some motorists who are befuddled by a Check Engine light will seek out the least painful (and cheapest) solution which is to take their vehicle to an auto parts store that offers a "free diagnosis." The diagnosis consists of plugging in a code reader into the DCL connector and reading out the code. The auto parts stores who offer a free diagnosis service say the code will usually reveal the nature of the problem so the motorist can decide what to do next. They're hoping, of course, that the motorist will buy a part from their store and install it themselves to fix their problem. And if that doesn't work, that the motorist will buy another part and install that in hopes it will solve the problem. And when that doesn't work, that the motorist will buy yet another part and install it themselves in hopes of fixing he problem. You get the picture.

Anyone who repairs late model vehicles today for a living knows that diagnosing complex emissions and driveability problems is not as simple as reading a code and replacing a part. OBD II is a great system that has a tremendous amount of self-diagnostic capability, but it only identifies faults in particular circuits or systems. It does not tell you which component to replace. That can only be determined after doing additional diagnostic work to isolate the fault.

Some problems such as misfires and evaporative emission (EVAP) leaks can be very challenging to nail down. Misfires can be caused by ignition problems, fuel problems or compression problems. The underlying cause might be fouled spark plugs, bad plug wires, a weak ignition coil, dirty injectors, a shorted or open injector, low fuel pressure, a vacuum leak, a leaky head gasket, burned exhaust valve or a camshaft with a bad lobe. No simple plug-in diagnosis will give you the answer until you do a lot of other checks.

To make matters worse, some of these friendly auto parts stores will also erase the code(s) after they've given their customer the diagnosis. Erasing the code turns out the MIL light -- at least temporarily -- which provides some relief for the poor motorist. But it may also make the job of diagnosing the fault harder if valuable diagnostic information that you might have needed was erased.

OBD II & EMISSIONS TESTING Another diagnostic issue that's becoming more of an issue with OBD II is that a growing list of states are now substituting an OBD II emissions test for a tailpipe test. The OBD II test is quick and easy, goes not require an expensive dyno or emissions analyzer, and gives a pass/fail indication in a minute or less. There's no risk of damage to the vehicle (as may be the case when running a vehicle on a dyno), and the reliability of the OBD II test is actually better than a tailpipe emissions test. Why? Because the OBD II system monitors emissions 24/7 365 days a year. There are no arbitrary cutpoints that can be fudged one way or the other to pass or fail more or less vehicles. Everybody dances to the same tune and must meet the same standards.

OBD II is also much better at detecting evaporative emissions leaks, and a drop off in converter efficiency. If the MIL light is on and there's a code for an EVAP or converter problem, you can usually bet the problem is real. The problem may not have any noticeable effect on driveability or performance, but technically it is in violation of the standards -- and must be fixed before the MIL light will go out and say out.

OBD II monitors evaporative emissions by checking for fuel vapor leaks once a drive cycle. OBD II does this by applying vacuum or pressure to the fuel tank, vapor lines and charcoal canister. If it detects no airflow when the EVAP canister purge valve is opened, or it detects a leakage rate that is greater than that which would pass through a hole 0.040 inches in diameter (0.020 inches for 2000 and up model year vehicles), it indicates a fault.

If you find a P0440 code that indicates a fuel vapor leak, finding the leak can be a challenge. The first place to start is the gas cap. A loose-fitting or damaged cap can allow enough air leakage to set a code. To find a leak in a vapor hose, you may need a leak detector that uses smoke and/or dye. A 0.020 inch hole is the size of a pin.

PLUG-IN DIAGNOSTICS

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All OBD II-equipped vehicles have a common J1962 16-pin diagnostic connector and use the same "generic" fault codes.

This means all you need is an OBD II-compliant code reader or scan tool to check readiness status, and to read and clear codes. The state emission programs require vehicle inspection facilities to use a more sophisticated plug-in tool that also records vehicle data for record keeping purposes, but otherwise they are using the same basic scan tool technology as everybody else.

To access the OBD II system all you have to do is plug a code reader or scan tool into the 16-pin connector (note: there are no "manual flash codes" on OBD II systems). The connector is usually located under the dash near the steering column. But on some vehicles, it can be hard to find. On many Hondas, the plug is located behind the ashtray. On BMW and VW, it is behind trim panels. On Volvo, the plug is next to the hand brake. On Audi, you'll find it hidden behind the rear seat ashtray.

THE OBD II PLUG-IN TEST An OBD II test is a simple plug-in computer check that verifies four things: 1. The Vehicle Identification Number (VIN).

2. That the vehicle's OBD II system is ready (all required readiness monitors have been set).

3. The status of the MIL lamp. The lamp must be functioning correctly and come on when commanded to do so.

Otherwise, it must be off indicating no codes.

4. That the vehicle has no diagnostic trouble codes that would cause the MIL lamp to come on.

OBD II monitors misfires, converter efficiency, catalyst heater (if used), the evaporative system, air injection system (if used), fuel trim, oxygen sensors, exhaust gas recirculation (if used), secondary air system (if used), the coolant thermostat (starting in 2000), positive crankcase ventilation system (starting in 2002) and even the A/C systems on some 2002 and newer vehicles.

If a situation develops in any of these monitored systems that could cause a real or potential emissions problem, OBD II will watch it, set a code and eventually illuminate the MIL. Most OBD II codes take time to mature and will not turn on the MIL lamp immediately. OBD II may wait until it detects the same problem on two separate drive cycles before it converts a pending code into a mature code and turns on the MIL lamp. The bottom line here is if the light is on, the vehicle will NOT pass an OBD II plug-in test. The problem must be fixed and the MIL light must stay out before the vehicle will pass.

READINESS ISSUES One of the EPA's requirements for using a plug-in OBD II check in lieu of a tailpipe test is to make sure the OBD II system has run all of its monitors and that the monitors have all passed. But there's a catch. Some import vehicles have readiness issues when it comes to setting all the OBD II monitors. Consequently, the EPA currently allows up to two readiness monitors not to be set prior to testing 1996 to 2000 model year vehicles, and one readiness readiness monitor for 2001 to 2003 vehicles.

When OBD II runs a self-check on a particular component or system, it lets you know by setting a readiness "flag" or indicator which can be displayed on your code reader or scan tool. If OBD II has run all the available monitors and all the monitors have passed -- and no faults have been found -- the vehicle should pass the OBD II plug-in test. But if all the required monitors have not run, the vehicle can't be given an OBD II test. The motorist must drive the vehicle and come back again, or take a tailpipe test if that is an option.

If OBD II detects a fault when running a monitor, the setting of a code may prevent the remaining monitors from running. A bad oxygen sensor, for example, will prevent the catalyst monitor from running. Getting all the monitors to run can be tricky on some vehicles. Each monitor has certain operating requirements that must take place before the self-check will run.

To set the converter monitor, for example, the vehicle may have to be driven a certain distance at a variety of different speeds. The requirements for the various monitors can vary considerably from one vehicle manufacturer to another, so there is no "universal" drive cycle that will guarantee all the monitors will be set and ready.

As a general rule, doing some stop-and-go driving around town at speeds up to about 30 mph followed by five to seven minutes of steady 55 mph highway speed driving will usually set most or all of the monitors. Consequently, if you're checking an OBD II system and discover that one or more of the monitors have not run, it may be necessary to test drive

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the vehicle to set the remaining monitors. With the EVAP monitor, the vehicle may require a certain period of inactivity (such as setting overnight) and certain ambient temperature conditions (such as above freezing) before the EVAP monitor will run.

Some vehicles with known readiness issues include 1996-98 Mitsubishi models (which require a very specific drive cycle), and 1996 Subaru and Volvo 850 Turbo (turning the key off clears all the readiness flags, so don't turn the vehicle off after driving). On 1997 Toyota Tercel and Paseo, the readiness flag for the EVAP monitor never will set, and no dealer fix is yet available. Other vehicles have often have a "not ready" condition for the EVAP and catalytic converter monitors include 1996-98 Volvo, 1996-98 Saab, and 1996-97 Nissan 2.0L 200SX.

DRIVE CYCLES If the MIL lamp comes on while driving, or remains on after starting the engine, it means OBD II has detected a problem.

The lamp will usually remain on -- unless the fault does not reoccur in three consecutive drive cycles that encounter the same operating conditions, or the fault is not detected for another 40 drive cycles. If OBD II sees no further evidence of the problem, it will turn off the MIL lamp and erase the code.

An OBD II drive cycle is not just turning the ignition key on and off or starting the engine. A drive cycle requires starting a cold engine and driving the vehicle until the engine reaches normal operating temperature. The next drive cycle doesn't begin until the engine has been shut off, allowed to cool back down and is restarted again. On some vehicles, the drive cycle also includes the cold soak time between trips. On some vehicles, the EVAP monitor won't run unless the vehicle has sit for eight hours. There no way to bypass or get around such requirements, so you have to do what ever the system requires. And if that means waiting, you have to wait.

READING DTC CODES If OBD II has detected a fault, you should find one or more "generic" codes (which start with the prefix "P0"), and maybe one or more "enhanced" codes (OEM specific codes that start with a "P1"). All OBD II compliant code readers and scan tools should be able to display generic codes, but some do not display all the OEM enhanced codes. As a result, you may not get the full picture of what's going on if you're using a tool with limited capabilities. The same goes for accessing many OBD II diagnostic features such as history codes, snapshot data, and special diagnostic test modes that require two-way communication and special scan tool software. For example, some of the OBD II diagnostic features that are currently accessible with an OEM factory scan tool are not yet available on aftermarket scan tools. This may limit your ability to diagnose and repair certain types of problems.

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An inexpensive Personal Digital Assistant (PDA) or smart phone with scanner software and cable, or even a DIY type of code reader can be used to read and clear most OBD II codes on 1996 and newer vehicles. This type of tool can often be used to make a quick diagnosis, and in many cases you don't need anything else. But for advanced diagnostics, you need a professional grade scan tool or software package with advanced capabilities.

For some jobs, you may also need a tool that can graph or display waveforms. That means buying a digital storage oscilloscope if you don't buy a high end scanner that can do both. Most scan tools display data stream values, which is what the PCM tells it to display. If the PCM is misreading a sensor input or is substituting bogus information, you have no way of knowing without actually testing the circuit or component in question. That's where a scope comes in handy.

When a scope is hooked up to a sensor or circuit, it shows what's actually going on inside that device or circuit. Voltage is displayed as a time-based waveform. Once you know how to read waveforms, you can tell good ones from bad ones. You can also compare waveforms against scan tool data to see if the numbers agree (which is a great way to identify internal PCM faults). A scope also allows you to perform and verify "action-reaction" tests. You can use one channel to monitor the action or input, and a second, third or fourth channel to watch the results. For example, you might want to watch the throttle position sensor, fuel injector waveform, crank sensor signal and ignition pattern when blipping the throttle to catch an intermittent misfire condition.

OnBoard Diagnostics II Guide for Windows XP, Vista or 7

A Quick Reference Guide for all 1996 & newer vehicles

Photo & screen captures: Bob Pattengale

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INTERPRETING GENERIC SCAN DATA

BY BOB PATTENGALE

Readily available ‘generic’ scan data provides an excellent foundation for OBD II diagnostics.

Recent enhancements have increased the value of this information when servicing newer vehicles.

I

f you don’t have a good starting point, driveability diagnostics can be a frustrating experience. One of the best places to start is with a scan tool. The question asked by many is, “Which scan tool should I use?” In a perfect world with unlimited resources, the first choice would probably be the factory scan tool.

Unfortunately, most technicians don’t have extra-deep pockets. That’s why my first choice is an OBD II generic scan tool. I’ve found that approximately 80% of the driveability problems I diagnose can be narrowed down or solved using nothing more than OBD II generic parameters. And all of that information is available on an OBD II generic scan tool that can be purchased for under $300.

The good news is the recent phase-in

of new parameters will make OBD II generic data even more valuable. Fig. 1 on page 54 was taken from a 2002 Nissan Maxima and shows the typical parameters available on most OBD IIequipped vehicles. As many as 36 parameters were available under the original OBD II specification. Most vehicles from that era will support 13 to 20 parameters. The California Air Resources Board (CARB) revisions to OBD II CAN-equipped vehicles will increase

the number of potential generic parameters to more than 100. Fig. 2 on page 56 shows data from a CAN-equipped 2005 Dodge Durango. As you can see, the quality and quantity of data has increased significantly. This article will identify the parameters that provide the greatest amount of useful information and take a look at the new parameters that are being phased in.

No matter what the driveability issue happens to be, the first parame-

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INTERPRETING GENERIC SCAN DATA

Fig. 1

ters to check are short-term fuel trim (STFT) and long-term fuel trim (LTFT). Fuel trim is a key diagnostic parameter and your window into what the computer is doing to control fuel delivery and how the adaptive strategy is operating. STFT and LTFT are expressed as a percentage, with the ideal range being within 5%. Positive fuel trim percentages indicate that the powertrain control module (PCM) is attempting to enrichen the fuel mixture to compensate for a perceived lean condition. Negative fuel trim percentages indicate that the PCM is attempting to enlean the fuel mixture to compensate for a perceived rich condition. STFT will normally sweep rapidly between enrichment and enleanment, while LTFT will remain more stable. If STFT or LTFT exceeds 10%, this should alert you to a potential problem.

The next step is to determine if the condition exists in more than one op-

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erating range. Fuel trim should be checked at idle, at 1500 rpm and at 2500 rpm. For example, if LTFT B1 is 25% at idle but corrects to 4% at both 1500 and 2500 rpm, your diagnosis should focus on factors that can cause a lean condition at idle, such as a vacuum leak. If the condition exists in all rpm ranges, the cause is more likely to be fuel supply-related, such as a bad fuel pump, restricted injectors, etc.

Fuel trim can also be used to identify which bank of cylinders is causing a problem. This will work only on bankto-bank fuel control engines. For example, if LTFT B1 is 20% and LTFT B2 is 3%, the source of the problem is associated with B1 cylinders only, and your diagnosis should focus on factors related to B1 cylinders only.

The following parameters could affect fuel trim or provide additional diagnostic information. Also, even if fuel trim is not a concern, you might find an indication of another problem

when reviewing these parameters: Fuel System 1 Status and Fuel System 2 Status should be in closedloop (CL). If the PCM is not able to achieve CL, the fuel trim data may not be accurate.

Engine Coolant Te m p e r a t u re (ECT) should reach operating temperature, preferably 190°F or higher. If the ECT is too low, the PCM may richen the fuel mixture to compensate for a (perceived) cold engine condition.

Intake Air Temperature (IAT) should read ambient temperature or close to underhood temperature, depending on the location of the sensor.

In the case of a cold engine check— Key On Engine Off (KOEO)—the ECT and IAT should be within 5°F of each other.

The Mass Airflow (MAF) Sensor, if the system includes one, measures the amount of air flowing into the engine. The PCM uses this information to calculate the amount of fuel that

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INTERPRETING GENERIC SCAN DATA

Fig. 2

should be delivered, to achieve the desired air/fuel mixture. The MAF sensor should be checked for accuracy in various rpm ranges, including wide-open throttle (WOT), and compared with the manufacturer’s recommendations. Mark Warren’s Dec. 2003 Driveability Corner column covered volumetric efficiency, which should help you with MAF diagnostics. A copy of that article is available at www.motor.com, and an updated volumetric efficiency chart is available at www.pwrtraining.com.

When checking MAF sensor readings, be sure to identify the unit of measurement. The scan tool may report the information in grams per second (gm/S) or pounds per minute (lb/min). For example, if the MAF sensor specification is 4 to 6 gm/S and your scan tool is reporting .6 lb/min, change from English units to metric units to obtain accurate readings.

Some technicians replace the sensor, only to realize later that the scan tool was not set correctly. The scan tool manufacturer might display the para-

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meter in both gm/S and lb/min to help avoid this confusion.

The Manifold Absolute Pressure (MAP) Sensor, if available, measures manifold pressure, which is used by the PCM to calculate engine load. The reading in English units is normally displayed in inches of mercury (in./Hg). Don’t confuse the MAP sensor parameter with intake manifold vacuum; they’re not the same. A simple formula to use is: barometric pressure (BARO) MAP intake manifold vacuum. For example, BARO 27.5 in./Hg MAP 10.5 intake manifold vacuum of 17.0 in./Hg. Some vehicles are equipped with only a MAF sensor, some have only a MAP sensor and some are equipped with both sensors.

Oxygen Sensor Output Voltage B1S1, B2S1, B1S2, etc., are used by the PCM to control fuel mixture. Another use for the oxygen sensors is to detect catalytic converter degradation.

The scan tool can be used to check basic sensor operation. Another way to test oxygen sensors is with a graphing

scan tool, but you can still use the data grid if graphing is not available on your scanner. Most scan tools on the market now have some form of graphing capability.

The process for testing the sensors is simple: The sensor needs to exceed .8 volt and drop below .2 volt, and the transition from low to high and high to low should be quick. In most cases, a good snap throttle test will verify the sensor’s ability to achieve the .8 and .2 voltage limits. If this method does not work, use a bottle of propane to manually richen the fuel mixture to check the oxygen sensor’s maximum output. To check the low oxygen sensor range, simply create a lean condition and check the voltage.

Checking oxygen sensor speed is where a graphing scan tool helps. Fig. 3 on page 57 and Fig. 4 on page 58 show examples of oxygen sensor data graphed, along with STFT, LTFT and rpm, taken from two different graphing scan tools.

Remember, your scan tool is not a lab scope. You’re not measuring the

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Fig. 3

sensor in real time. The PCM receives the data from the oxygen sensor, processes it, then reports it to the scan tool. Also, a fundamental OBD II generic limitation is the speed at which that data is delivered to the scan tool. In most cases, the fastest possible data rate is approximately 10 times a second with only one parameter selected. If you’re requesting and/or displaying 10 parameters, this slows the data sample rate, and each parameter is reported to the scan tool just once per second. You can achieve the best results by graphing or displaying data from each oxygen sensor separately. If the transition seems slow, the sensor should be tested with a lab scope to verify the diagnosis before you replace it.

Engine Speed (RPM) and Ignition Timing Advance can be used to verify good idle control strategy.

Again, these are best checked using a graphing scan tool.

The RPM, Vehicle Speed Sensor (VSS) and Throttle Position Sensor (TPS) should be checked for accuracy.

These parameters can also be used as reference points to duplicate symptoms and locate problems in recordings.

Calculated Load, MIL Status, Fuel Pressure and Auxiliary Input Status (PTO) should also be considered, if they are reported.

Additional OBD II Parameters Now, let’s take a look at the more recently introduced OBD II parameters.

These parameters were added on 2004 CAN-equipped vehicles, but may also be found on earlier models or nonCAN-equipped vehicles. For example, the air/fuel sensor parameters were available on earlier Toyota OBD II vehicles. Fig. 2 was taken from a 2005 Dodge Durango and shows many of the new parameters. Parameter descriptions from Fig. 2 are followed by the general OBD II description: FUEL STAT 1 Fuel System 1 Status: Fuel system status will display more than just Closed Loop (CL) or Open Loop (OL). You might find one

of the following messages: OL-Drive, indicating an open-loop condition during power enrichment or deceleration enleanment; OL-Fault, indicating the PCM is commanding open-loop due to a system fault; CL-Fault, indicating the PCM may be using a different fuel control strategy due to an oxygen sensor fault.

ENG RUN TIME Time Since Engine Start: This parameter may be useful in determining when a particular problem occurs during an engine run cycle.

DIST MIL ON Distance Traveled While MIL Is Activated: This parameter can be very useful in determining how long the customer has allowed a problem to exist.

COMMAND EGR EGR_PCT: Commanded EGR is displayed as a percentage and is normalized for all EGR systems. EGR commanded OFF or Closed will display 0%, and EGR commanded to the fully open

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Fig. 4

position will display 100%. Keep in mind this parameter does not reflect the quantity of EGR flow—only what the PCM is commanding.

EGR ERROR EGR_ERR: This parameter is displayed in percentage and represents EGR position errors.

The EGR Error is also normalized for all types of EGR systems. The reading is based on a simple formula: (Actual EGR Position Commanded EGR) Commanded EGR EGR Error. For example, if the EGR valve is commanded open 10% and the EGR valve moves only 5% (5% 10%) 10% 50% error. If the scan tool displays EGR Error at 99.2% and the EGR is commanded OFF, this indicates that the PCM is receiving information that the EGR valve position is greater than 0%. This may be due to an EGR valve that is stuck partially open or a malfunctioning EGR position sensor.

EVAP PURGE EVAP_PCT: This parameter is displayed as a percentage and is normalized for all types of purge systems. EVAP Purge Control

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commanded OFF will display 0% and EVAP Purge Control commanded fully open will display 100%. This is an important parameter to check if the vehicle is having fuel trim problems. Fuel trim readings may be abnormal, due to normal purge operation. To eliminate EVAP Purge as a potential contributor to a fuel trim problem, block the purge valve inlet to the intake manifold, then recheck fuel trim.

FUEL LEVEL FUEL_PCT: Fuel level input is a very useful parameter when you’re attempting to complete system monitors and diagnose specific problems. For example, the misfire monitor on a 1999 Ford F-150 requires the fuel tank level to be greater than 15%. If you’re attempting to duplicate a misfire condition by monitoring misfire counts and the fuel level is under 15%, the misfire monitor may not run. This is also important for the evaporative emissions monitor, where many manufacturers require the fuel level to be above 15% and below 85%.

WARM-UPS WARM_UPS: This parameter will count the number of warm-ups since the DTCs were cleared.

A warm-up is defined as the ECT rising at least 40°F from engine starting temperature, then reaching a minimum temperature of 160°F. This parameter will be useful in verifying warm-up cycles, if you’re attempting to duplicate a specific code that requires at least two warm-up cycles for completion.

BARO BARO: This parameter is useful for diagnosing issues with MAP and MAF sensors. Check this parameter KOEO for accuracy related to your elevation.

C AT TMP B1S1/B2S1

CATEMP11, 21, etc.: Catalyst temperature displays the substrate temperature for a specific catalyst. The temperature value may be obtained directly from a sensor or inferred using other sensor inputs. This parameter should have significant value when checking catalyst operation or looking at reasons for premature catalyst failure, say, due to overheating.

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Fig. 5

CTRL MOD (V) VPWR: I was surprised this parameter was not included in the original OBD II specification. Voltage supply to the PCM is critical and is overlooked by many technicians. The voltage displayed should be close to the voltage present at the battery. This parameter can be used to look for low voltage supply issues. Keep in mind there are other voltage supplies to the PCM. The ignition voltage supply is a common source of driveability issues, but can still be checked only with an enhanced scan tool or by direct measurement.

ABSOLUT LOAD LOAD_ABS: This parameter is the normalized value of air mass per intake stroke displayed as a percentage. Absolute load value ranges from 0% to approximately 95% for normally aspirated engines and 0% to 400% for boosted engines. The information is used to schedule spark and EGR rates, and to determine the pumping efficiency of the engine for diagnostic purposes.

OL EQ RATIO EQ_RAT: Commanded equivalence ratio is used to determine the commanded air/fuel ratio of the engine. For conventional oxygen sensor vehicles, the scan tool should display 1.0 in closed-loop and the PCM-

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commanded EQ ratio during openloop. Wide-range and linear oxygen sensors will display the PCM-commanded EQ ratio in both open-loop and closed-loop. To calculate the actual A/F ratio being commanded, multiply the stoichiometric A/F ratio by the EQ ratio. For example, stoichiometric is a 14.64:1 ratio for gasoline. If the commanded EQ ratio is .95, the commanded A/F is 14.64 0.95 13.9 A/F. TP-B ABS, APP-D, APP-E, COMMAND TAC: These parameters relate to the throttle-by-wire system on the 2005 Dodge Durango of Fig. 2 and will be useful for diagnosing issues with this system. There are other throttle-by-wire generic parameters available for different types of systems on other vehicles.

There are other parameters of interest, but they’re not displayed or available on this vehicle. Misfire data will be available for individual cylinders, similar to the information displayed on a GM enhanced scan tool. Also, if available, wide-range and linear air/fuel sensors are reported per sensor in voltage or milliamp (mA) measurements.

Fig. 5 above shows a screen capture from the Vetronix MTS 3100 Mastertech. The red circle highlights the “greater than” symbol (>), indicating that multiple ECU responses differ in

value for this parameter. The blue circle highlights the equal sign (=), indicating that more than one ECU supports this parameter and similar values have been received for this parameter.

Another possible symbol is the exclamation point (!), indicating that no responses have been received for this parameter, although it should be supported. This information will be useful in diagnosing problems with data on the CAN bus.

As you can see, OBD II generic data has come a long way, and the data can be very useful in the diagnostic process.

The important thing is to take time to check each parameter and determine how they relate to one another.

If you haven’t already purchased an OBD II generic scan tool, look for one that can graph and record, if possible. The benefits will immediately pay off. The new parameters will take some time to sort out, but the diagnostic value will be significant. Keep in mind that the OBD II generic specification is not always followed to the letter, so it’s important to check the vehicle service information for variations and specifications.

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