The Dreaded Check Engine Light

Why did it come on? What does it mean? How do I turn it off?

by David “Sam” Luttrell Jr, Absolute Automotive LLC

Most, if not all of us, have seen the dreaded “Check Engine” or “Service Engine Soon” message illuminate on the dash. This is called a “Malfunction Indicator Light” (MIL).

They first appeared in vehicles in the early 1980s. The automotive industry started adding computers to help control exhaust emissions and to improve fuel economy.

Over the years, more and more computer systems have been added, making our vehicles much more sophisticated and complex. They control everything from creature comforts to parking the car for us.

So why did your light come on?

The main computer, sometimes called the Powertrain Control Module (PCM), monitors and controls the way your engine, transmission, and emissions system operate. The PCM monitors a multitude of sensors for information on things like how far you have pushed the gas pedal, to the amount of air that is entering the engine.

The PCM also controls many electromechanical devices based on the information these sensors provide.

When the PCM detects a sensor that is out of its normal operating range, or one of the electro-mechanical devices malfunctioning, the PCM then sets and stores an “Error Code” and turns on the MIL.

What does it mean?

There are a multitude of possible “Error Codes” the PCM can set, it seems almost as many as there are stars in the sky. Some codes are for minor issues, like a loose gas cap, but an Error Code can also signal major issues that can cause engine or exhaust system damage. A flashing MIL indicates a more immediate concern, like an engine misfire happening at that moment.

How do I turn it off?

You will need a Code Reader or Scanner to access the PCM to read the stored codes. There are a variety of cheap code readers for the DIY's, and much more capable scanners for the professional diagnostic technicians.

Most automotive parts stores will read the error codes for free and clear them for you. Should the error code return, I urge you to take your vehicle to a professional automotive diagnostic technician.

Please understand that if your PCM set a code, for example, an Oxygen Sensor code, that does not necessarily mean the Oxygen Sensor is bad, only that it has detected too much, or too little oxygen in the exhaust flow.

I hope that this explanation of why the Check Engine Light illuminates is helpful. Please feel free to contact me at sam@absoluteautomotive.net if you have any questions or I can help in any way.