Malfunction Indicator Lamp: Description and Operation

MALFUNCTION INDICATOR LAMP (MIL)
The MIL is the only lamp that is controlled directly by the Powertrain Control Module (PCM), all other indicator lamps/gauges are controlled by the Body Control Module (BCM), or the Instrument Panel Cluster (IPC).

The Malfunction Indicator Lamp (MIL) is located on the instrument panel (CHECK ENGINE) or (SERVICE ENGINE SOON). The MIL performs the following functions:
^ It informs the driver that a problem has occurred and that the vehicle should be taken for service as soon as possible.
^ As a bulb check and system check, the MIL will illuminate with the ignition switch on and the engine not running. when the engine is started, the MIL will turn off. If the MIL remains on, the self-diagnostic system has detected a problem. If the problem goes away, the MIL will turn off in most cases, but a diagnostic trouble code will remain stored.
^ If the MIL is illuminated, then the engine stalls, the MIL will remain illuminated so long as the ignition switch is on.
^ If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled off, then on.

SERVICE VEHICLE SOON indicator
The following components may control the SERVICE VEHICLE SOON indicator:
^ The Electronic Brake Control Module/Electronic Brake Traction Control Method (EBCM/EBTCM)
^ The Powertrain Control Module (PCM)
^ The Body Control Module (BCM)

The SERVICE VEHICLE SOON indicator will turn on for approximately 3 seconds during the engine start-up for a bulb check. The SERVICE VEHICLE SOON indicator will turn on in order to warn the driver that a malfunction exists within the following systems:
^ ABS
Refer to Antilock Brake System.
^ BCM
Refer to Body Control Module.
^ PCM
Refer to Computers and Control Systems. Computers and Control Systems

This condition may degrade the overall vehicle performance.