The CHECK ENGINE or SERVICE ENGINE SOON dashboard warning lamp is referred to as the Malfunction Indicator Lamp (MIL). The lamp is connected to the engine control assembly and will alert the driver to certain malfunctions within the EEC system. When the lamp is lit, the PCM has detected a fault and stored an identity code in memory. The engine control system will usually enter either a failure or limited operation mode and driveability will be impaired.
The light will stay on as long as the fault causing it is present. Should the fault self-correct, the MIL will extinguish, but the stored code will remain in memory.
Under normal operating conditions, the MIL should light briefly when the ignition key is turned ON. As soon as the PCM receives a signal that the engine is cranking, the lamp will be extinguished. The dash warning lamp should remain out during the entire operating cycle.