Engine Control Module: Description and Operation

Powertrain Control Module (PCM):

The Powertrain Control Module (PCM) is located in the engine compartment.

The ignition system is controlled by the PCM.

NOTE: Base ignition timing by rotation of distributor is not adjustable on any of these engines.

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.

Speed Control Operation
The speed control electronic control circuitry is integrated into the PCM. 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 For Speed Control System for more information. The PCM cannot be repaired and must be replaced if faulty.

PCM Control of Automatic Transmission
The PCM controls operation of the converter clutch, overdrive clutch, and governor pressure solenoid. The control module determines transmission shift points based on input signals from the transmission thermistor, transmission output shaft speed sensor, crankshaft position sensor, vehicle speed sensor, throttle position sensor, and battery temperature sensor.