Description & Operation
The Powertrain Control Module (PCM) is a digital computer containing a microprocessor.
The PCM receives 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.PCM Ground
Ground is provided through multiple pins of the PCM connector. Depending on the vehicle there may be as many as three different ground pins. There are power grounds and sensor grounds. The power grounds are used to control the ground side of any relay, solenoid, ignition coil or injector. The signal ground is used for any input that uses sensor return for ground, and the ground side of any internal processing component.
The SBEC III case is shielded to prevent RFI and EMI. The PCM case is grounded and must be firmly attached to a good, clean body ground. Internally all grounds are connected together, however there is noise suppression on the sensor ground. For EMI and RFI protection the case is also grounded separately from the ground pins.
The PCM engine control strategy prevents reduced idle speeds until after the engine operates for 200 miles If the PCM is replaced after 200 miles of usage, update the mileage and vehicle identification number (VIN) in the new PCM. Use the DRB scan tool to change the mileage and VIN in the PCM. If this step is not done a Diagnostic Trouble Code (DTC) may be set. The PCM attaches to a bracket welded on the dash panel.PCM Inputs
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 generator charge rate by adjusting the generator field. The PCM also performs diagnostics.
The PCM adjusts injector pulse width (air-fuel ratio) based on the following inputs:
The PCM adjusts ignition timing based on the following inputs:
The PCM also adjusts engine idle speed through the idle air control motor based on the following inputs:
The Auto Shutdown (ASD) and fuel pump relays are located in the Power Distribution Center (PDC).
The camshaft position sensor and crankshaft position sensor signals are sent to the PCM. If the PCM does not receive the signal within approximately 1 second of engine cranking, it deactivates the ASD relay and fuel pump relay. When these relays are deactivated, power is shut off from the fuel injectors, ignition coils, oxygen sensor heating elements and fuel pump.
The PCM contains a voltage converter that changes battery voltage to a regulated 9 volts direct current to power the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5-volt direct current supply for the manifold absolute pressure sensor, throttle position sensor, and A/C pressure switch.
Removal & Installation
- Remove the air cleaner lid, disconnect the inlet air temperature sensor and makeup air hose.
- Remove the negative battery cable.
- Remove screws attaching PCM to dash panel bracket.
- Unlock the connector then disconnect both 40-way connectors from the PCM.
- Lift PCM up to remove it from vehicle.
- Install PCM. Tighten mounting screws to 10.7 Nm (95 inch lbs.).
- Attach both 40-way connectors to PCM. Lock the tabs.
- Install the negative battery cable.
Install the air cleaner lid; connect the inlet air temperature sensor and makeup air hose.