Mil Always On: Description

WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

The Malfunction Indicator Lamp (MIL) is used to indicate to the driver of the vehicle that an engine control system condition has occurred that may cause an increase in emissions and/or cause a driveability concern.

When the ignition is first turned ON the Powertrain Control Module (PCM) will illuminate the MIL for a bulb and system check. When the engine is started and operating the PCM will turn the MIL OFF if no DTCs are set.

The Alternative Fuel Engine Control Module (AF ECM) connects into the normal MIL control circuit path and does not affect the PCM operation of the MIL. The AF ECM is connected into the MIL control circuit path in order to command the MIL ON when a CNG DTC sets. Both the AF ECM and the PCM simultaneously test certain DTCs regardless of the fuel system that is in operation and may illuminate the MIL.

The instrument panel gauge fuse supplies the positive voltage source for the MIL. The PCM and/or the AF ECM can supply the ground path.