System Operation

SYSTEM OPERATION
The Check Engine or Malfunction Indicator Lamp (MIL) gives an indication when the Powertrain Control Module (PCM) has recorded a Diagnostic Trouble Code (DTC) for an On-Board Diagnostics II (OBDII) emissions-related circuit or component malfunction.

The lamp is controlled by the PCM. The PCM sends a lamp-on signal for about three seconds when the ignition switch is turned to the On position as a bulb test. Following the bulb test, the PCM uses inputs from many emissions-related circuits and sensors, along with its internal programming, to decide whether a condition exists that requires the MIL lamp to be turned on.

The MIL lamp can also be used to display a stored DTC by flashing on and off. Refer to Powertrain Management/Computers and Control Systems for more information on the PCM or the PCM inputs.