![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/fd914aec3c94ced9a34441e8c3858349.jpg?width=720&quality=85%2C50)
19 minute read
Intermittent problem detection strategies
![Publisher avatar for EndeavorBusinessMedia-VehicleRepairGroup](https://photo.isu.pub/t/endeavor-business-media/automotive-group-migrated/photo_large.jpg)
from Auto Service Professional - December 2019
by EndeavorBusinessMedia-VehicleRepairGroup
Problem solving tips By Bill Fulton
SSomeone once said that a good technician is not expensive but, rather, priceless.
Having said that, I note we have all spent way too much time on an intermittent problem to justify the hours spent on these types of problems.
So you drove the vehicle for 20 to 30 minutes without a single stumble or symptom. It happens to all of us. Our best hope is that although the service we’re performing may not turn out to be all that pro t- Figure 1: A DVOM’s Peak Detect mode will capture able, at least we retain a good and record a 100 millisecond signal drop-out. customer. ere have been many perature and at what speed. In they don’t want to pay a techtimes in my own experiences addition, when you have the nician to guess. But what do we where I have nally duplicated MIL on, did you take the time do when we can’t get the vehithe symptom and nally nar- to analyze and duplicate the cle to act up? Is there a pattern rowed down the problem and freeze frame conditions? failure or a silver bullet? xed it. Later on I go home and Many times during my live Can this be honestly comthink about the tests I could seminars I compare an auto- municated to the car owner? I have done, might have done or motive technician to a medi- have had to do it many times — should have done that would cal doctor. Suppose you have with success. have cut down the time on my a medical problem and you Have you ever addressed diagnostics. go to your primary care doc- an intermittent lean code, and tor and you give him a com- a er reading the freeze frame First things rst! plete and accurate description nd out that it occurred unHave you ever documented of your symptom. In the real der steady road load condithe symptom based on what world he most o en is going to tions? e MAF sensor has the car owner stated only to write a prescription for you to been replaced. e fuel trims nd out that it was not an ac- try and see if you get any im- are double digit positive at all curate description of the actual provement. at is what we call load conditions. e fuel pressymptom? In addition, how practicing medicine. sure specs are good and all the many times have you needed to Are we as technicians any sensor values are within specs. speak directly to the car owner di erent from the medical Making certain E-85 fuel was to nd out how o en the symp- doctor? I don’t think so. How- not used in a non- ex-fuel tom occurs and at what tem- ever, in the customer’s mind vehicle, can you honestly rec28
INTERMITTENT PROBLEM DETECTION STRATEGIES
ommend we try to chemically clean the injectors through the rail?
Did you catch the keyword here? We stated that we could try an injector cleaning process. It is certainly worth a try and can be the cure. But in reality can you guarantee a positive result?
Always keep in mind that we are technicians and not magicians. How many times were you forced to make a diagnostic guess based on tech tips or maybe a silver bullet? I have heard some instructors make the statement that they test and don’t guess. In the real world this simply doesn’t always hold water, especially when dealing with a very random and intermittent problem. There are certainly pattern failures on every make and model so we all investigate these pattern failures.
Case studies The first case study that I want to share with you involves a 2001 Honda Accord with a good crank and intermittent no start. When I arrived at the shop the work order stated exactly that — an intermittent no start.
I was faced with an issue where the shop owner did not get complete information from the car owner.
Figure 2: A DSO can prove invaluable in network checking.
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/4b21f020c4b747d443dfe82d6e37bf21.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/63505fe39a1bd8f8a40439e2be10ae62.jpg?width=720&quality=85%2C50)
Figure 3: A normal class 2 signal is a 7V to .2V signal. 7 volts indicates that a module is talking and .2 volts indicate an at rest condition.
I successfully started the Accord at least 20 times with no problems found. After doing a complete network test I found no codes at all.
Plan B required a call to the car owner. After interrogating the car owner I found out that the crank and intermittent no start occurred after the car had set in the summer sun with the windows up. The interior heats up and can cause the solid state main relay located
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/6ec2fdbea5cf8f4c18fb97841077f93c.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/b684c593b5f18eeb9605a7bc500ad77c.jpg?width=720&quality=85%2C50)
the main relay could be the fault.
Many of you know that this is in fact is a pattern failure on these vehicles.
In addition, the ignition switches can also cause the same symptom but not necessarily after a hot soak in the sun.
Where do we go? Is there anything wrong with being honest with the car owner? We cannot duplicate the symptom. Can we recommend trying a main relay? Have you been down this road before?
In summary, the car owner pinpoint the exact cause. Did we jump on the pattern failure band wagon? Not until we obtained the specific info from the car owner who stated that the crank no start always occurred after a prolonged hot sun hot soak condition with the windows up. There are cases where you may find a crack in the circuit board with a magnifier.
Know your limitations The second rule we must cover is to know the strengths Figure 4: Note how the voltage floats well above the logic .2V rest value during cranking attempt. and limits of your diagnostic equipment. In cases of electriunder the dash to heat up and justify in making a diagnostic prime weapon. All DVOMs are expand the solid state board guess in replacing the main not created equally, so in this and create an open. The solid relay? presentation we will use the state main relay powers up the In closing, that is exactly Fluke series 87 DVOM. CKP and the CMP sensors on what I replaced. With my The reason being is that the this car. communication with the car Peak Detect mode will capture
Since I could not duplicate owner he fully understood that and record a 100 millisecond the symptom I was forced into since I could not duplicate the signal drop out. It can also demaking a diagnostic guess that problem I simply could not tect a 1 millisecond signal drop
cal problems the DVOM is our stated that the crank and no Figure 5: Starting circuit schematic. The first dynamic start always occurred after an extended hot soak in the summer sun with the windows up. voltage check was done at V1. This should be battery voltage from the ignition switch in the crank position. The #2 reading is where the PCM ground side controls the starter enable relay. Reading #3 shows good dynamic Do we have enough clues to voltage from the power side of the starter relay. 30
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/cd6df265dbbc2759aff40b4744724073.jpg?width=720&quality=85%2C50)
out by pressing the button under the Peak Detect button (see Figure 1).
We all have utilized the wiggle test and by using this meter function, the meter will beep when a signal dropout occurs from a poor connection.
When recalling the Min/Max values simply press the Min/Max button once and the Max recorded values will be displayed. Pressing the Min/Max button the second time will display the Min values. is is where you will see the signal drop out. Pressing the Min/Max button the third time will give us the average signal value. e Min/Max mode works on all meter functions.
Without this valuable mode we would be dealing with trying to see a voltage change on the digital readout with a slow 4 times-per-second update rate.
Whenever doing a voltage check we should always make sure the circuit is active and loaded instead of disconnecting the component.
When doing an open circuit voltage a DVOM will not properly load the circuit, say as a normal load from a fuel pump. e meter only requires 22 micro amps of current ow when open circuit testing a component. When doing this test in checking for good dynamic voltage with the component loading the circuit as in the fuel pump circuit we should always use the fuel pump ground wire for our negative meter lead. If both power and ground circuits are OK we should drop the full 12 volts across the fuel pump.
Let’s say the meter shows 7.2 volts. e problem is either weak supply voltage or resistance in the ground circuit. In addition, it may be a good idea to utilize the Min/Max mode of the meter and perform a wiggle test.
Many technicians have turned a blind eye for the need of a DSO (digital storage oscilloscope), see Figure 2. I simply disagree. Let’s take a look at a late model Cadillac with an intermittent nocrank condition.
A er performing a network test we found a laundry list of codes from pretty much all of the on-board modules. is vehicle is equipped with the GM Pass Key the deterrent system which in fact will lock out the starter with a fault. Since multiple modules agged a network of U series codes, we suspected a corrupted network. With a DSO probing the Class 2 network at pin 2 of the DLC we found this signal in Figure 3. A normal class 2 signal is a 7V to .2V signal. Seven volts
AUTOMOTIVE INTELLIGENCE
WORK SMARTER NOT HARDER
MS908S
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/a89e26d858866e2f0ab4b048be1f1c1f.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/13fd81c32e53503663e983b3db90522e.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/c4b05850745855cd8a642e974cdf140d.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/324131af3bb9609b7800f8218a44046d.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/c127e1e5d2907cada61e95e0cf38a0ec.jpg?width=720&quality=85%2C50)
MS908SP
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/63a1f00766f72c3c05a08e8ef5d78895.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/0b3074d61c362cc35f8227558d4a7758.jpg?width=720&quality=85%2C50)
DIAGNOSTIC INTELLIGENCE
64G Memory
POWERFUL HARDWARE / SMARTER SOFTWARE
Phone: (855) 288-3587 USSUPPORT@AUTEL.COM AUTEL.COM • MAXITPMS.COM• MAXISYSADAS.COM ©2019 Autel Intelligent Technology Corp., Ltd. All Rights Reserved
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/676db810e3e46e8907b65160814f2319.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/4f88411d9d112d02d1a55c5901a45ffc.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/276154a0a82761521bf5317803ad610c.jpg?width=720&quality=85%2C50)
Note Figure 4 during a cranking attempt. See how the voltage floats well above the logic .2V rest value? We have to suspect a bad ground somewhere in the ground circuit.
Note the starting circuit schematic in Figure 5. The first dynamic voltage check was done at V1. This should be battery voltage from the ignition switch in the crank position. The #2 meter reading is where the PCM ground side controls the pull in windings of the starter enable relay.
Since this ground is controlled by a transistor inside the PCM, the voltage should go below .4V which told us that the PCM is seeing a good en-
then grounded to the body from the ground cable shown in Figure 6. With the battery located under the back seat the negative battery cable bolts directly to a body ground. With a negative jumper cable clamped to the block and routed to the negative battery terminal we ran a redundant ground circuit from the block to the battery negative terminal. The engine cranks over and now starts every time. The ground cable between the engine block and body was at Figure 6: In this example, the block is grounded fault. to the body via a ground cable. Tests revealed that the ground connection was faulty. Many of our really good technicians know the diagmeans that a module is talking Meter reading #3 is check- amp probe interfaced with a and .2V is at rest. This is what is ing for good dynamic voltage DSO. The attenuation setting referred to as a pulse train sig- from the power side of the I use most often is every 100 nal. Every module on the class starter relay and showed good millivolts =1 amp (see Figure 2 network supplies its own 7V dynamic voltage. With good 7). bias voltage. Notice where the meter reading so far we know Another problem vehicle voltage slightly rises above the that the starter gets its ground was a 2001 Ford Ranger with .2V rest value during KOEO. thru the block. The block is an intermittent hard start
nostic value of a low inductive able signal from the theft de- Figure 7: The attenuation setting I use most often terrent module. is every 100 millivolts equals 1 amp. 32 ASP December 2019
complaint. Upon my arrival at the shop the vehicle was in the bay and started just fine. The technician had attached a fuel pressure gauge which showed a good 35 psi. When the vacuum line was disconnected from the fuel pressure regulator the fuel pressure jumped to 45 psi.
I requested a phone call to the truck owner to obtain specifically when the hard starting problem occurred. He stated it occurred after an overnight cold soak. The injector on-time to start a cold Figure 9: On most PFI systems the on-line amperage values engine at 35 degrees Fahren- will range between 4 and 6 amps with uniform oscillations. heit is over 100 milliseconds. The injector on-time to start truck owner. With a current vision. The attenuation facup a fully warmed PFI system probe attached around one tor on the amp probe is set is around 5 milliseconds. The wire at the inertia switch we at 100 millivolts = 1 amp. So longer the injector on-time, obtained the amperage wave- simple math tells us that every the more stress on the fuel form indicated in Figure 8. vertical division on the DSO pump to deliver the fuel pres- The waveform was captured would represent 5 amps per sure and volume needed to during a KOEO key cycle. division. start a cold engine. Note the voltage per division Note that the initial current
We explained this to the is set at 500 millivolts per di- surge is over 25 amps. Note that after the initial current surge we lost continuity and the amps fell to 0 for a brief period of time. Then the amperage value peaked again at about 20 amps and then finally settled in at over 8 amps with a very unstable waveform. I communicated my findings with the truck owner and informed him he has a very bad fuel pump and it could easily be the cause of the cold starting problem. The truth is we cannot continue with any more testing until we have the OK to replace the pump. Given the OK from the truck owner, the fuel pump was replaced with happy reFigure 8: With a current probe attached around one wire at the inertia switch in this example, the amperage waveform sults. Whenever faced with a was obtained during a KOEO key cycle on a Ford Ranger. potential fuel pump problem
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/a2c74d7e8463c0de4a79a65e8388e7b1.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/92d5a7ae63eaa6566aab2742ff383a70.jpg?width=720&quality=85%2C50)
chanical integrity of the fuel pump. Normally on most PFI systems the on-line amperage values will range between 4 and 6 amps with good uniform oscillations (see Figure 9).
Access to the fuel pump circuit can be obtained at the fuel pump fuse by using a fusible jumper or by removing the fuel pump relay and jumping across the power terminal.
Another intermittent problem was on a GM Express Van with an intermittent P0316 crank sensor code. An intermittent miss and stall symptom followed by an intermittent no-start condition also existed.
DREF signal (rpm signal — distributor reference). is is one sensor input that cannot be substituted or the one we allow to disallow. Looking at the DREF signal in Figure 12 we see the problem. e DREF signal is breaking up. ere are pattern failures here where the main bearings wear which destroys the air gap between the tip of the crank sensor and the reluctor. is mechanical interference can cause an erratic signal from the crank sensor. A visual inspection on the Figure 10: T-shaped pins found at discount or craft tip of the crank sensor indi-stores work well for connector probing. cated no physical interference we initially decide we need to the shop. e crank sensor the reluctor wheel. check fuel pressure. had been replaced two times Now note the schematic in
GM is the only manufac- before with no good results. Figure 13. e signal circuit turer that still gives us a fuel Notice the secondary ignition from the crank sensor to the pressure test port. e amper- wave form in Figure 11. Did PCM is color coded yellow. We age value obtained by current- you notice the missing point simply ran a redundant circuit ramping the fuel pump will of primary turn on? With that between the crank sensor sigshow us the electrical and me- in mind let’s scope check the nal circuit to the PCM. Anoth-
between the crank sensor and e vehicle had been towed Figure 11: Note the secondary ignition waveform on the GM in twice before I arrived at Express Van. Note the missing point of primary turn-on.
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/ca106f957a1b2bd96d3f6b4644a4452e.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/48022d12f8c6b033e62bc245f8cb6c7e.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/ffb0dec12624f41d999f37d17d8154b1.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/3f3ff5d560e767147884b5364caa9d76.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/b92a784b8bc4ca2de7446c05b7168511.jpg?width=720&quality=85%2C50)
Figure 12: On the same Express Van, we see the DREF signal breaking up. This may be due to worn crank main bearings causing the air gap at the crank position sensor to change.
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/42d5f07a23abee2a473cd01354504bcf.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/ee8ebb8818049ebca00d35e4b148b97a.jpg?width=720&quality=85%2C50)
Figure 13: The Express Van schematic. The signal circuit from the crank sensor to the PCM is coded yellow. Running a redundant circuit between the sensor and the PCM cured this vehicle’s problem.
er happy ending. Circuit access to a component has always been a trial. When back-probing a connector, I have found that the T-shaped pins available in the sewing department from your local discount stores work great (see Figure 10).
As we stated earlier, running a redundant circuit is usually a good exercise. In addition, there have been many cases where terminal fretting occurs causing an intermittent bad connection of a sen-
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/7e9468084f70d8ecb8d34fe1c82365e5.jpg?width=720&quality=85%2C50)
sor or output device. Terminal fretting is caused by vibration between the male and female terminal, causing the metal to ake o resulting in an intermittent poor connection. e key is to clean the terminals and to apply a dab of stabilant 22A which is a contact enhancer and will pretty much guarantee conductivity. is product is available from your local parts store. e BWD part number is CL85 (see Figure 14).
Many times the round female terminals lose their tension to their male counter parts resulting in a loss of connection. A set of wire size drill bits are available from the folks at Granger. Wire size drill bits from 57 thru 60 pretty much covers most automotive applications (see Figure 15). By running the shank end of the drill into the female terminal you are basically doing a drag test in checking the female terminal tension. In ad-
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/58abf4b6a58577251a348f9f61a37f48.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/011320a75d5ee3f497ae6cff13964905.jpg?width=720&quality=85%2C50)
dition you are most certainly cleaning the inners of the female terminal.
In closing, I can’t say enough of the importance of questioning the car owner as to what is the exact symptom and when does it most o en occur. Is it temperature related and does it occur at a certain speed? Since most car owners don’t speak our language, help them out by asking speci c questions in the king’s language.
In the real world we can’t over-emphasize that all too o en we must experience the symptom on our own. You simply can’t say enough about what you feel through the seat of your pants during a test drive. When the symptom occurs while under road load conditions be sure to take the scan tool and utilize the record function.
Keep your eyes on the road and your nger on the record button. Upon returning to the shop to review the recorded data, be sure to use the graphic mode of the scan tool to view several seconds of data. When looking at data on a digital readout you are looking at one small moment in time. is may give you a good direction to begin your diagnostics.
Until next time, good luck in your diagnostic dilemmas. ■
Bill Fulton is the author of Mitchell 1’s Advanced Engine Performance Diagnostics and Advanced Engine Diagnostics manuals. He is also the author of several lab scope and drivability manuals such as Ford, Toyota, GM, and Chrysler OBD I and OBD II systems, Fuel System Testing, many other training manuals in addition to his own 101 Lab Scope Testing Tips. He is a certified Master Technician with over 30 years of training and R&D experience. He was rated in the top three nationally in Motor Service Magazine’s Top Technical Trainer Award and has instructed for Mitchell 1, Precision Tune, OTC, O’Reilly Auto Parts, BWD, JD Byrider, Snap-on Vetronix and Standard Ignition programs. You may have also seen Fulton in many Lightning Bolt Training videos and DVDs and read his articles in many auto service magazines. He currently owns and operates Ohio Automotive Technology, which is an automotive repair and research development center.
FROM THE FIRST FILL TO THE LAST.
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/8221f5db309e464adb8ca1072bf31a9f.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/07ddf91acbd47681be49331b4141de9e.jpg?width=720&quality=85%2C50)
![](https://assets.isu.pub/document-structure/201007133244-4aa5211c73dc5f95df7c9a4a701d6945/v1/3f8c183766cc9ff3d8ff4794dbb97e61.jpg?width=720&quality=85%2C50)
PENTOSIN FLUIDS ARE DESIGNED TO MEET THE STRICT OE STANDARDS OF THE WORLD’S FINEST IMPORTS.
CHECK OUT OUR FULL LINEUP OF HIGHQUALITY FLUIDS AT PENTOSIN.NET OR VISIT OUR ONLINE CATALOG AT SHOWMETHEPARTS.COM/CRP.