Your cars check engine light is part of the onboard diagnostics system or OBD. The computer in your car will monitor and control the vehicles performance and regulate such items as ignition timing, fuel mixture, engine speed and can even tell your automatic transmission when to shift.
When the OBD system comes across a problem it cannot adjust it will have the computer turn on a warning light or check engine light and store the code in the computers memory. These trouble codes will help in identifying the cause of the problem such as a misfiring engine or a bad sensor. In order to read the code you will need to have a scanning tool or take it to your local automotive repair shop or dealer. Car manufacturers used the OBD system originally to aid technicians in troubleshooting and pinpointing the malfunction in the vehicle. What the OBD system looks for will depend on the year, make, and model of the vehicle.
The original computer system in a vehicle varied widely in there capabilities and most systems would only check the various electronic sensors to make sure they were hooked up and working. When the OBD II systems came out federal regulations made it mandatory that all auto manufactures were to install this system into their vehicles. Its main purpose was to act like a built in emission monitoring station that would alert you if a problem has occurred in your emission system. If there is a problem, your check engine light will come on and cannot be turned off until a scanner is hooked up and the problem is diagnosed.