Is Your Check Engine Light On?

At L& M we treat your check engine light a little differently than most shops and dealerships, we will perform a computer scan at no charge to determine the code, we will then advise any necessary diagnostics needed. Most times there are common known fault codes that can be repaired with very little diagnostic charges; simple test will usually determine the source of the fault. Ignoring a check engine light may adversely affect engine performance and economy, or worse, engine damage.  If, however, you would like us to reset the light and drive the vehicle to determine if the code is intermittent that is OK with us. Read on to find out more.   

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.

When the service engine soon light is turned on the computer is notifying the driver that there is a malfunction and a code, or multiple codes set. The computer will usually check itself twice, confirming the fault before turning on the light.

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.

Does this mean that replacing the oxygen sensor would turn off the light? The answer is in most cases, replacing the sensor will not turn the light off.

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 malfunctioning system properly will save you money and time in avoiding replacing unnecessary parts. Using our automotive scan tool, we can view the data stream for the particular sensors related to the fault to determine the malfunction.

To review your computer is watching multiple channels and multiple sensors and is simply comparing the data with the parameters that have been programmed. Above or below, these data settings, commands the PCM to notify the driver.

Clearing the codes may turn out the light temporally but is not resolving the fault the computer has determined.