Malfunction Indicator Lamp: Description and Operation

Malfunction Indicator Lamp (MIL)

The MIL notifies the driver that the powertrain control module (PCM) has detected an OBD emission-related component or system fault. When this occurs an OBD diagnostic trouble code (DTC) will be set.

^ The MW is located in the instrument cluster and is labeled CHECK ENGINE SERVICE ENGINE SOON or the ISO standard engine symbol.
^ The MIL is illuminated during the instrument cluster prove out for approximately 4 seconds.
^ For applications with a dedicated hard wire MIL circuit the PCM will illuminate the MIL until a profile ignition pickup (PIP) signal is detected. For 2OO5 the following vehicles use a hard wire circuit: Crown Victoria/Grand Marquis Explorer Sport Trac and Ranger.
^ The MIL will remain illuminated after instrument cluster prove out if:
^ an emission related concern and DTC exists.
^ no PIP signal is detected (applications with a dedicated hard-wire MIL circuit). The PIP signal is generated in the PCM using the crankshafi position (CKP) sensor. For these applications the MIL can be helpful in diagnosing a no start.
^ the PCM does not send a control message to the instrument cluster (applications with the MIL controlled through the communication link).
^ the PCM is operating in the Hardware Limited Operation Strategy (KLOS).
^ the MIL circuit is shorted to ground (applications with a dedicated hard wire MIL circuit).
^ The MIL remains off during the instrument cluster prove out if:
^ an indicator or instrument cluster concern is present.
^ the MIL circuit is open (applications with a dedicated hard wire MIL circuit).
^ To turn off the MIL afier a repair a reset command from the diagnostic tool must be sent or 3 consecutive drive cycles must be completed without a fault.
^ For all MIL concerns go to Symptom Charts.
^ If the MIL flashes at a steady rate a severe misfire condition may exist.
^ If the MIL flashes erratically the PCM can reset while cranking if the battery voltage is low.