Check engine light

The check engine light on cars is a very sensitive warning device. In this quick article I will discuss why the engine light comes on and also the easiest way to turn it off.

The warning light is turned on directly by the car's computer, which most manufacturers call the PCM. This stands for power train control module. You may find other names for this device, but basically it is considered the car's main computer.

The PCM monitors the many different automotive engine sensors. It divides the sensors into multiple channels and monitors each channel and compares the range of data to the specifications that are burned in memory.

Check engine light comes on

An example of why the check engine light comes on would be an oxygen sensor code. The range of operation that the computer is looking for is between 50 and 800 mV.

In this specific example, the computer is also monitoring the changes in the voltage. If the oxygen sensor returns data that is out of this range, the check engine light is turned on to notify the driver of a problem.

The reason that the service engine light is on is because the sensor is out of range. This may be because the sensor is faulty, but more than likely, the sensor is operating correctly and is out of range due to an air fuel mixture problem.

This is where diagnosing the malfunction properly will save you money and time in replacing unnecessary parts. Using an automotive scan tool, you can view the data stream for the particular sensors related to air fuel mixture.

Another good rule of thumb when diagnosing an oxygen sensor code is to diagnose the other codes that are set, prior to diagnosing the oxygen sensor code. This is because the oxygen sensor code may have been set, due to another system failure that affects the data that the oxygen sensor sends and PCM monitors.

Check engine light on cars

In some cases, these out of range, readings, are either temporary or intermittent. This is again where the scan tool comes in handy for figuring out why the check engine light is illuminated.

You can clear check engine light codes and run the vehicle and see if the service engine light comes back on. If it does, then you have a path of diagnosis related to the codes that have returned.

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