All cars since 1988 and many prior to that year have some sort of check engine light that will come on briefly when the ignition is turned on, and when the car senses their is an emission control failure. It is linked to the on board diagnostics system(OBD 1 and in 1996, OBD2) that regulates and records the actions of the various emission controls in today's computer controlled cars. The check engine light itself is the warning light that car owners will see ignited when the system detects a failure, anything from a gas cap not screwed on tight enough to a malfunctioning catalytic converter.
It is important to note that when this light comes on, there is no danger of an engine failure. The car will continue to run, it just might not be running at optimal efficiency. In addition, the car will not pass a smog inspection with the light on, regardless of how clean it's running. As cars age, the light can become more burdensome and require a code reader to diagnose the problem. The code reader is plugged into the OBD port and then displays fault a code that tells the mechanic what system is not working or not working correctly. This code may or may not be the car's actual problem, as many mechanics will tell you that the computer does not always detect the correct problem.
Sometimes the light can be reset by disconnecting the car battery for a brief period of time. Other times it will shut itself off if it fails to detect the problem after a given amount of time. Some of the newer systems actually record what triggered the light and then will store it in the car's memory, things like a cylinder misfiring.
