Cherokee 4WD L6-4.0L VIN S (1998)
Powertrain Control Module: Description and Operation
SYSTEM OPERATION
Powertrain Control Module (PCM) Location
The Powertrain Control Module (PCM) is located in the engine compartment.
NOTE: Base ignition timing by rotation of distributor is not adjustable.
The PCM opens and closes the ignition coil ground circuit to operate the ignition coil. This is done to adjust ignition timing, both initial (base) and
advance, and for changing engine operating conditions.
The amount of electronic spark advance provided by the PCM is determined by five input factors: engine coolant temperature, engine rpm, intake
manifold temperature, manifold absolute pressure and throttle position.
The speed control electronic control circuitry is integrated into the Powertrain Control Module (PCM). The PCM is located in the engine
compartment. The PCM speed control functions are monitored by the On-Board Diagnostics (OBD). All OBD sensed systems are monitored by
the PCM. Each monitored circuit is assigned a Diagnostic Trouble Code (DTC). The PCM will store a DTC in electronic memory for certain
failures it detects. See On-Board Diagnostic Test. The PCM cannot be repaired and must be replaced if faulty.
