The Powertrain Control Module (PCM) receives input signals from various switches and sensors. Based on these inputs, the PCM regulates various engine and vehicle operations through different system components. These components are referred to as Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs to the PCM are considered Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm, manifold absolute pressure, engine coolant temperature, throttle position, transmission gear selection (automatic transmission), vehicle speed and the brake switch.
The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle position, vehicle speed, transmission gear selection, engine coolant temperature and from inputs it receives from the air conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator charge rate through control of the generator field and provides speed control operation.
Removal & Installation
- Disconnect the negative battery cable.
Unplug the 38-way connectors from the PCM.
NOTEA locating pin is used in place of one of the mounting bolts.
- Pry the clip from the locating pin.
- Remove the two remaining mounting bolts.
Remove the PCM from the vehicle.
Position the PCM to the body and install the two mounting bolts.
NOTEPosition the ground strap in place before tightening the mounting bolts.
- Install the clip to the locating pin.
- Tighten the mounting bolts to 35 inch lbs. (4 Nm).
- Carefully plug in the 38-way connectors to the PCM.
- Connect the negative battery cable.
- Use a diagnostic scan tool to reprogram the PCM with the VIN and original mileage if PCM has been replaced.
- Start the engine and allow it to reach normal operating temperature. Using a diagnostic scan tool, check for the presence of any Diagnostic Trouble Codes (DTCs). Record and address these codes as necessary.
- Refer to any Technical Service Bulletins (TSBs) that may apply.
- Review the scan tool Freeze Frame information. If possible, try to duplicate the conditions under which the DTC set.
- With the engine running at normal operating temperature, monitor the scan tool parameters related to the DTC while wiggling the wire harness. Look for parameter values to change and/or a DTC to set. Turn the ignition off.
Visually inspect the related wire harness. Disconnect all the related harness connectors. Look for any chafed, pierced, pinched, partially broken wires and broken, bent, pushed out, or corroded terminals. Perform a voltage drop test on the related circuits between the suspected inoperative component and the PCM.
CAUTIONDo not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool no. 8815 to perform diagnosis.
- Inspect and clean all PCM, engine, and chassis grounds that are related to the most current DTC.
- If numerous trouble codes were set, use a wire schematic and look for any common ground or supply circuits.
- For any Relay DTCs, actuate the Relay with the scan tool and wiggle the related wire harness to try to interrupt the actuation.
- For intermittent Evaporative Emission trouble codes perform a visual and physical inspection of the related parts including hoses and the Fuel Filler cap.
- Use the scan tool to perform a System Test if one applies to failing component. A co-pilot, data recorder, and/or lab scope should be used to help diagnose intermittent conditions.