A malfunction indicator lamp (MIL), commonly referred to as the "Check Engine Light", is a warning lamp to indicate malfunction of a computerized engine management system. It is found on the instrument panel of most automobiles. When illuminated, it is typically either an amber or red color. On vehicles equipped with OBD II diagnostics, the light has two stages: steady indicating a minor fault such as a loose gas cap or failing sensor and flashing indicating a severe fault, that will eventually destroy the catalytic converter, such as a misfire. When the MIL is lit, the engine control module stores a fault code related to the malfunction, which can be retrieved with a diagnostic scan tool and used for further diagnosis. The malfunction indicator lamp usually bears the legend check engine, service engine soon, or a picture of an engine.
If a fault occurs during a test cycle the lamp will illuminate. It takes 3 test cycles with a fault detected in each cycle to come on if failure is of a performance nature. The lamp will illuminate on 1 failure during a test cycle with a safety related fault. In some cases the is a warning indicator that may be of a more minor nature, however many cases delay in checking can result in a much more expensive repair in the future. Most repair facilitys offer an inexpensive test to inform you of your options. There are also auto parts stores that will "pull codes" for free but many times the individual doin this does not have the technical exspertise to understand what is found. Beware of the "free check" as it does in many cases become expensive.
If you MIL indicator is on, please don't just ignore. It has something really important to tell you. Your vehicles life may just depend on it.