Check Engine Light: What Does it Mean?

MECHANIC
Close up hands of unrecognizable mechanic doing car service and maintenance.(standret | Getty Images/iStockphoto)

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Everyone hates to start their car and see the dreaded check engine light come on. By the end of this article, I hope to help you understand the process it takes to correct this problem. I also would like to bust the myth that there is a machine that you plug into the vehicle that tells you everything that’s wrong with the vehicle.

First, what is a check engine light? The check engine light is a warning light that the ECM (Engine Control Module) turns on when it detects a problem. The United States Government passed a law that requires the light to come on only for catalyst damaging or pollution. Some manufacturers have implemented settings that will turn the light on for other problems also. There are over 100 codes that can be stored in a vehicle and more than 3 times that amount for manufacturers’ specific codes.

What is the machine that you use to work on this problem? This machine is a scan tool. A simpler or cheaper version is also known as a code reader. The scan tool reads codes and provides information in real time on how the sensors are reading. It also allows us control over some systems in the vehicle. The code reader style only reads the Government Regulated Generic Codes. This reader may not show you the code that is currently stored in your vehicle.

What is a code? A code is a 4-digit number preceded by a letter. This letter corresponds to which computer set the problem. For example: P0301 refers to a misfire on #1 cylinder. At this point it is a mechanic’s job to find out why it is misfiring. Is it a spark plug, a coil, spark plug wires, fuel, or internal engine damage? You could also have damage to the wire harness, or the computer may be broken and can’t fire the spark plug or deliver the fuel.

In conclusion, when your check engine light comes on, we use a scan tool to ask the computer what’s wrong. In return, the ECM gives us a code that signals a sensor not working or a sensor that has the wrong information. This scan tool only reports what is not working but not why it’s not working. As a mechanic, we have several years of training and education to find out the why.

At White’s Automotive, every mechanic has undergone training to thoroughly understand and diagnose engine problems.

Be sure to read our article next month because I’ll be diving deeper into the diagnostic procedure. I’ll go over why your vehicle can have the same symptoms but have 2 different problems.

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