Powertrain Control Module: Description: Operation
The Powertrain Control Module (PCM) is a digital computer containing a microprocessor (Fig 1) and (Fig 2). The PCM receives input signals from various switches and sensors referred to as Powertrain Control Module Inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices referred to as Powertrain Control Module Outputs.
- Air Conditioning Pressure Transducer
- ASD Relay
- Battery Voltage
- Brake Switch
- Camshaft Position Sensor
- Crankshaft Position Sensor
- Distance Sensor (from transmission control module)
- EGR Position Feedback (if equipped)
- Engine Coolant Temperature Sensor
- Heated Oxygen Sensors
- Ignition sense
- Inlet Air Temperature Sensor
- Knock Sensor
- Leak Detection Pump Feedback
- Manifold Absolute Pressure (MAP) Sensor
- Park/Neutral (from trans range sensor)
- PCI Bus
- Power Steering Pressure Switch
- Proportional Purge Sense
- SCI Receive
- Speed Control
- Throttle Position Sensor
- Transaxle Control Module (2.7L Only)
- Transmission Control Relay (Switched B+) (2.4L Only)
- Transmission Pressure Switches (2.4L Only)
- Transmission Temperature Sensor (2.4L Only)
- Transmission Input Shaft Speed Sensor (2.4L Only)
- Transmission Output Shaft Speed Sensor (2.4L Only)
- Torque Management Input (From TCM) (2.7L Only)
- Transaxle Gear Engagement (From TCM)
- Vehicle Speed
- Air Conditioning Clutch Relay
- Automatic Shut Down (ASD) and Fuel Pump Relays
- Data Link Connector (PCI and SCI Transmit)
- Double Start Override
- EGR Solenoid (if equipped)
- Fuel Injectors
- Generator Field
- High Speed Fan Relay
- Idle Air Control Motor
- Ignition Coils
- Leak Detection Pump
- Natural Vacuum Leak Detection
- Low Speed Fan Relay
- MTV Actuator
- Proportional Purge Solenoid
- SRV Valve
- Speed Control Relay
- Speed Control Vent Relay
- Speed Control Vacuum Relay
- Torque Reduction Request
- Transmission Control Relay (2.4L Only)
- Transmission Solenoids (2.4L Only)
- 8 Volt Output (SBEC controlled vehicles)
- 5 Volt Output
Based on inputs it receives, the powertrain control module (PCM) adjusts fuel injector pulse width, idle speed, ignition timing, and canister purge operation and EGR if equipped. The PCM regulates the cooling fans, air conditioning and speed control systems. The PCM changes generator charge rate by adjusting the generator field.
The PCM adjusts injector pulse width (air-fuel ratio) based on the following inputs.
- Manifold Absolute Pressure
- Engine Speed (crankshaft position sensor)
- Battery Voltage
- Inlet Air Temperature Sensor
- Engine Coolant Temperature
- Exhaust Gas Oxygen Content (heated oxygen sensors)
- Throttle Position
The PCM adjusts engine idle speed through the idle air control motor based on the following inputs.
- Brake Switch
- Engine Coolant Temperature
- Engine Speed (crankshaft position sensor)
- Park/Neutral (
- Transaxle Gear Engagement
- Throttle Position
- Vehicle Speed (from Transmission Control Module) (SBEC controlled vehicles)
The PCM adjusts ignition timing based on the following inputs.
- Inlet Air Temperature
- Engine Coolant Temperature
- Engine Speed (crankshaft position sensor)
- Knock Sensor
- Manifold Absolute Pressure
- Park/Neutral (from trans range sensor)
- Transaxle Gear Engagement
- Throttle Position
The automatic shut down (ASD) and fuel pump relays are mounted externally, but turned on and off by the powertrain control module.
The camshaft and crankshaft signals are sent to the powertrain control module. 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, power is shut off to the fuel injectors, ignition coils, fuel pump and the 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, and crankshaft position sensor. The PCM also provides a regulated 5.0 volts supply for the, manifold absolute pressure sensor, throttle position sensor and EGR (if equipped).
The PCM engine control strategy prevents reduced idle speeds until after the engine operates for 320 km (200 miles). If the PCM is replaced after 320 km (200 miles) of usage, update the mileage in new PCM. Use the DRBIII® scan tool to change the mileage in the PCM. Refer to the POWERTRAIN DIAGNOSTIC PROCEDURES article and the DRBIII® scan tool. If equipped with SKIM, must use SKIM function to program VIN number in new PCM.