If your car was manufactured after 1996, it has an OBD II system that monitors emissions and other systems on board. While it’s primarily focused on emissions, it can also report other problems that are only peripherally related to emissions (engine misfires, for instance). It communicates any potential problems to the driver through a single light in the dash – the Check Engine Light, also called the MIL or Malfunction Indicator Lamp.

Is the Check Engine Light the only connected light?

Yes. The only way your OBD system has to communicate with you is through the Check Engine Light. What’s more, the other lights in your dash are NOT connected to the OBD system (although advanced scan tools can access the car’s computer and read many of these trouble codes via the OBD II connector under the dash).

Common reasons the Check Engine Light is illuminated

If your Check Engine Light flashes on right after the engine cranks, and then turns off again, this is normal. This is the self-check procedure, and the OBD system letting you know that it’s operating.

If the Check Engine Light comes on and stays on, it means that the computer has identified a problem that has some sort of impact on emissions. These can range from engine misfires to failed oxygen sensors, dead catalytic converters and even a loose gas cap. You’ll need to have the code pulled by a mechanic to begin the diagnostic process and determine the cause of the problem.

If the Check Engine Light comes on and begins flashing, it means that your engine is experiencing significant misfires, and that the catalytic converter could overheat as a result, causing a fire. You should immediately stop the car and have a mechanic diagnose and repair the problem.

While the OBD system can only use the Check Engine Light to communicate with you, it’s vital that you pay attention to that light and know what to do.

This article originally appeared on YourMechanic.com as Are Lights the Only Thing the OBD Uses to Warn the Driver of Issues? and was authored by Valerie Johnston.


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