Engine Control Module: Description and Operation

SYSTEM OPERATION

Powertrain Control Module:

The PCM regulates the ignition system. The PCM supplies battery voltage to the ignition coil through the Auto Shutdown (ASD) Relay. The PCM also controls the ground circuit for the ignition coil (2.4L). By switching the ground path for the coil on and off, the PCM adjusts ignition timing to meet changing engine operating conditions.

On a 2.5L The PCM controls ignition timing by turning on and off a transistor in the distributor. Refer to 2.5L Ignition Coil for more information.

During the crank-start period the PCM maintains spark advance at 9° BTDC. During engine operation the following inputs determine the amount of spark advance provided by the PCM.
- Intake air temperature
- Coolant temperature
- Engine RPM
- Intake manifold vacuum
- Knock sensor (2.4L Engines)
The PCM also regulates the fuel injection system.

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 any failure it detects. See On-Board Diagnostic Tests for more information. The PCM cannot be repaired and must be replaced if faulty.

USE THE DRB SCAN TOOL TO REPROGRAM THE NEW PCM WITH THE VEHICLES ORIGINAL IDENTIFICATION NUMBER (VIN) AND THE VEHICLES ORIGINAL MILEAGE. IF THIS STEP IS NOT DONE A DIAGNOSTIC TROUBLE CODE (DTC) MAY BE SET.