Cherokee 4WD L6-4.0L VIN S (1998)
Malfunction Indicator Lamp: Description and 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 instrument cluster circuitry based upon messages received from the PCM on the Chrysler Collision Detection (CCD) data bus.
The PCM sends a lamp-on message 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 PCM then sends the proper message to the instrument cluster on the
CCD data bus to turn the lamp on or off.
The MIL lamp can also be used to display a stored DTC by flashing on and off. Refer to Powertrain Management/Computer and Control Systems
for more information on the PCM or the PCM inputs. Refer to Powertrain Management/Computer and Control Systems for more information on
DTCs and their retrieval.
