The heart of the electronic control system, which is found on the vehicles covered by this guide, is a Powertrain Control Module (PCM). The Powertrain Control Module (PCM) is a digital computer containing a microprocessor. The PCM recieves input signals from various switches and sensors that are referred to as PCM inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices that are referred to as PCM outputs. It may also control the shift functions of the electronically controlled automatic transmission.
Care must be taken when handling these expensive components in order to protect them from damage. Carefully follow all instructions included with the replacement part. Avoid touching pins or connectors to prevent damage from static electricity.
Based on inputs it receives, the PCM adjusts fuel injector pulse width, idle speed, ignition spark advance, ignition coil dwell and EVAP canister purge operation. The PCM regulates the cooling fan, air conditioning and speed control systems. The PCM changes the alternator charge rate by adjusting the alternator field. The PCM also performs diagnostic functions.
The Automatic ShutDown (ASD) relay and fuel pump relay are mounted in the Power Distribution Center (PDC), but turned on and off by the PCM. The camshaft and crankshaft signals are sent to the PCM. If the PCM does not receive both signals within approximately one second of engine cranking, it deactivates the ASD and fuel pump relays. When these relays are deactivated, the power is shut off to the fuel injectors, ignition coils, fuel pump and heating element in each oxygen sensor.
The PCM contains a voltage converter that changes battery voltage to a regulated 8.0 volts. The 8.0 volts power the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5.0 volt supply for the engine coolant temperature sensor, manifold absolute pressure sensor and throttle position sensor.
REMOVAL & INSTALLATION
See Figures 1, 2, 3 and 4
- Disconnect the negative battery cable first, then the positive battery cable.
- Remove the two Power Distribution Center (PDC)-to-mounting bracket screws.
- Remove the battery from the vehicle.
- Turn the PDC toward the center of the vehicle to remove from the rear mounting bracket.
- Push the PDC rearward to remove it from the front mounting bracket. Lay the PDC aside, allowing access to the Powertrain Control Module (PCM).
- Disengage the two 40-way connectors from the PCM by squeezing the tabs on each side of the connector and pulling rearward.
- Remove the 3 screws mounting the PCM to the inner fender.
- Remove the PCM from the vehicle.
- Install the PCM into the vehicle in the proper position and tighten the 3 mounting screws.
- Attach the two 40-way connectors to the PCM.
- Install the PDC into its original position and secure with the 2 mounting screws.
- Install the battery into the vehicle.
- Connect the positive battery cable first, then connect the negative battery cable.