The Check Engine Light (which is actually the Malfunction Indicator Lamp or MIL) alerts you when a problem occurs in the engine control system. Depending on the nature of the problem, the Check Engine Light may come on and go off, remain on continuously or flash. Some intermittent problems will make the Check Engine Light come on only while the fault is occurring. When the problem goes away, the Check Engine Light goes off. Other types of problems will turn the Check Engine Light on, and it will remain on until the fault is diagnosed and repaired.

The Check Engine Light can be annoying because it seems to have a mind of its own. The Check Engine Light also tells you nothing about the problem. It might be something serious - or it might not. There is no way to know until you diagnose the vehicle. So you don't know if you should stop immediately or ignore the Check Engine Light and keep on driving.

If no other warning lights are on, and the engine seems to be running normally (no unusual noises, smells, vibrations, etc.), you can assume the fault that is causing the Check Engine Light to come on is probably minor and won't hinder your ability to continue driving. But if other warning lights are on, you should stop and investigate the problem.

When the Check Engine Light comes on, a diagnostic trouble code (DTC) is recorded in the on-board computer memory that corresponds to the fault. Some problems can generate more than one trouble code, and some vehicles may have multiple problems that set multiple trouble codes.