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Check Engine Light (CEL), Service Engine Soon (SES), Engine Light ON¦ What Does It Mean?

In this introductory article we will answer some basic questions such as; “Why did it illuminate?  What does it mean when it illuminates? Can I continue driving the car? Will it harm anything else?”

Why did the Engine Light (CEL), Service Engine Soon (SES), Engine Light illuminate?

The Check Engine Light (CEL), Service Engine Soon (SES), or Engine Light illuminates when the Powertrain Control Module (PCM) computer detects a situation that increases the vehicles emissions beyond the acceptable limits imposed by the U.S. Clean Air Act of 1971. The Powertrain Control Module (PCM) is programmed to compensate for normal wear and tear but it does have limits.

What does it mean when Check Engine Light (CEL), Service Engine Soon (SES), Engine Light illuminates?

It means that the Powertrain Control Module (PCM) has reached its’ adaptive limits or only has testing capability on a specific vehicle’s emission systems in which the tested specific emissions system has failed the test.

Here are two situation examples of those limits being exceeded;

1.. A fuel filter that is so clogged from lack of maintenance or extremely dirty fuel that the engine is starving for fuel. In this situation the Powertrain Control Module (PCM) can compensate for lack of fuel until its’ limits are exceeded. This usually results in what is termed a multi trip failure and the Powertrain Control Module (PCM) illuminates the Check Engine Light (CEL), Service Engine Soon (SES), Engine Light upon a repeat of the detected failure.

2.. A fuel (gas) cap that fails to seal or was left off after refueling which allows vapors from the tank to escape. In this situation the Powertrain Control Module (PCM) can only test the integrity of the system but has no way to compensate. This is termed a one trip failure and the Powertrain Control Module (PCM) illuminates the Check Engine Light (CEL), Service Engine Soon (SES), Engine Light immediately.

Can I continue driving the car?

Through the implementation of Onboard Diagnostics II (OBD II) the manufacturers have given us some ways to make an informed decision. Through the observation of the Check Engine Light (CEL), Service Engine Soon (SES), or Engine Light we may be able to determine if it is a one trip or multi trip failure. Some manufacturers have implemented other programming strategies into the Powertrain Control Module (PCM) called Limp In or Default Strategies Mode. In Limp In or Default Strategies Mode some manufacturers limit the top speed the vehicle will drive or limit the automatic transmission to 2nd gear only of the forward gears. This Limp In or Default Strategies Mode is the manufacturers way of forcing you to take the car in for inspection, service and repair.

The Check Engine Light (CEL), Service Engine Soon (SES), or Engine Light has 4 states of operation.

  The first is a bulb check when the key is cycled to on position but the car is not running.

  The second is when the vehicle is running and the Check Engine Light (CEL), Service Engine Soon (SES), or Engine Light is flashing very fast.

  The third is when the vehicle is running and the Check Engine Light (CEL), Service Engine Soon (SES), or Engine Light is illuminated constantly. On any restart it returns to illuminated state immediately.

  The fourth is just like the third, except on restarts the Check Engine Light (CEL), Service Engine Soon (SES), or Engine Light remains off for an amount of time then illuminates and remains on until the next restart and the process repeats.

It is always advisable to at the very least to obtain a Diagnostic Trouble Code (DTC) check. This is usually a free service offered by retail parts stores. They do this in the hope of selling the parts necessary to repair the car. The DTCs that they will retrieve for you are all Powertrain codes and are in the form of Pxxxx (P followed by 4 numbers). It is advisable to write these numbers down but DO NOT Clear them or the Freeze Frame data stored in the Powertrain Control Module (PCM).

The basic DTC check described above is simply an indication and not hard evidence of what may be wrong. A thorough diagnostic including any Freeze Frame data needs to be performed to verify what the problem is and what has caused it so that the root cause can be repaired thus avoiding a repeat situation.

Will it harm anything else?

In example 1 above the Check Engine Light could have been flashing or staying on for a few minutes then going off which could have resulted in misfire situation. This misfire situation could possibly result in a Diagnostic Trouble Code for a failed Oxygen Sensor. Either of these two Engine Light states can cause serious damage to the Catalytic Converter or other components.

In example 2 above the Service Engine Soon Light could have been on constantly and there would not be any harm to the car.

As you can see the answer is not clear until some further diagnostics are performed. Just using the Diagnostic Trouble Code for the Oxygen Sensor without further diagnosis could have resulted in replacing good parts. So when the Check Engine Light (CEL), Service Engine Soon (SES), or Engine Light illuminates watch for the different states of illumination and any other clues that might help. But do not just ignore it.

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All above information is based on published information as of 01/2015 or products purchsed to confirm
 

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