The Malfunction Indicator Lamp MIL

The malfunction indicator lamp (MIL) alerts the driver that the powertrain control module (PCM) has detected an OBD II emission-related component or system fault. When this occurs, an OBD II Diagnostic Trouble Code (DTC) will be set.

The MIL is located on the instrument cluster and is labeled CHECK ENGINE, SERVICE ENGINE SOON or ISO standard engine symbol.

Power is supplied to the MIL whenever the ignition switch is in the RUN or START position.

The MIL will remain on in the RUN/START mode as a bulb check for approximately 4 seconds.

If the MIL remains on after the bulb check:

  • The PCM illuminates the MIL for an emission related concern and a DTC will be present
  • The instrument cluster will illuminate the MIL if the PCM does not send a control message to the instrument cluster
  • The PCM is operating in the Hardware Limited Operation Strategy (HLOS)
  • The MIL circuit is shorted to ground

If the MIL remains off (during the bulb check):

  • Bulb is damaged
  • MIL circuit is open

To turn off the MIL after a repair, a reset command from the Scan Tool must be sent, or three consecutive drive cycles must be completed without a fault.

  • If the MIL blinks at a steady rate, a severe misfire condition could possibly exist
  • If the MIL blinks erratically, an intermittent open B+ to the bulb or an intermittent short to ground in the MIL circuit exist. Also, the PCM can reset while cranking if battery voltage is low

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