The Malfunction Indicator Lamp (MIL) looks similar to the lamp used on earlier vehicles (i.e., the Check Engine or "Service Engine Soon lamp). However, on OBD II systems, the MIL is activated under a strict set of guidelines that dictate that the lamp must be turned on when the PCM detects an emissions related fault that could impact the vehicle tailpipe emissions or Evaporative Loss system.
The Malfunction Indicator Lamp (MIL) lamp is mounted in the instrument panel. It provides several functions as described below:
To inform the driver that a fault affecting vehicle emission levels has occurred and to bring the vehicle in for service immediately.
To check the bulb and related circuit, the MIL will is turned on with the key in the "on" position with the engine off (KOEO). Once the engine is started, the MIL should go out.
If the MIL remains on with the engine running, or if a fault is suspected due to an emissions related problem, an OBD System Check of the PCM diagnostics should be performed. The tests contained in this diagnostic procedure will help find any faults that might not be detected using other diagnostic routines.