Malfunction Indicator Lamp: Description and Operation

The Malfunction Indicator Lamp (MIL) illuminates to alert the driver that the Powertrain Control Module (PCM) has detected an OBD-II emission related component or system malfunction. When this occurs, a Diagnostic Trouble Code (DTC) will be set.

When a malfunction has been detected in two consecutive drive cycles, a DTC will be stored in the PCM, and the MIL will be turned ON. The MIL will be turned OFF after three consecutive drive cycles have been completed without the same malfunction detected. The DTC will be erased from Keep Alive Memory (KAM) after 40 warm-ups without the malfunction being detected. The only exception to this is if a misfire occurs that could cause damage to the catalyst. It this event, the MIL will illuminate immediately or may flash.

The MIL is labeled "CHECK ENGINE". Power is supplied to the MIL whenever the ignition switch is in the ON or START position. The MIL will remain ON in the ON or START position as a bulb check until the Camshaft Position (CMP) is detected. The light may also illuminate due to a short to ground in the MIL circuit, or vehicle operation in the Hardware Limited Operation Strategy (HLOS). In addition, The MIL will remain ON if it was ON when the vehicle was last shut down. If the MIL does not turn OFF while the engine is cranking, it could indicate that the PCM is not receiving the CMP signal or that the MIL circuit is shorted to ground. If the MIL blinks, there is a severe misfire, or an intermittent short to ground in the MIL circuit.

To reset the MIL after a repair, a PCM reset command must be sent from a scan tool, or three consecutive drive cycles must be completed without a malfunction.