Powertrain Control Module: Description: Notes
The Powertrain Control Module (PCM) is a digital computer containing a microprocessor. See Fig 1. 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
- Ambient temperature Sensor
- ASD Relay
- Battery Temperature Sensor (NGC)
- Battery Voltage
- Brake Switch
- Camshaft Position Sensor
- Crankshaft Position Sensor
- EGR Position Feedback
- Engine Coolant Temperature Sensor
- Heated Oxygen Sensors
- Ignition sense
- Intake Air Temperature Sensor
- Knock Sensor
- NVLD Assembly
- Manifold Absolute Pressure (MAP) Sensor
- Park/Neutral
- PCI Bus
- Power Steering Pressure Switch
- EVAP Purge Return
- SCI Receive
- Speed Control
- Throttle Position Sensor
- Transmission Control Relay (Switched B+)
- Transmission Pressure Switches
- Transmission Temperature Sensor
- Transmission Input Shaft Speed Sensor
- Transmission Output Shaft Speed Sensor
- Transaxle Gear Engagement
- 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
- Fuel Injectors
- Generator Field
- High Speed Fan Relay
- Idle Air Control Motor
- Ignition Coils
- NVLD Assembly
- Low Speed Fan Relay
- MTV Actuator
- EVAP Purge
- SRV Valve
- Speed Control Vent Solenoid
- Speed Control Vacuum Solenoid
- 5 Volt Output
- Torque Reduction Request
- Transmission Control Relay
- Transmission Solenoids
- Vehicle Speed
Based on inputs it receives, the powertrain control module (PCM) adjusts fuel injector pulse width, idle speed, ignition timing, and canister purge operation. 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.
- Battery Voltage
- Intake Air Temperature Sensor
- Engine Coolant Temperature
- Engine Speed (crankshaft position sensor)
- Exhaust Gas Oxygen Content (heated oxygen sensors)
- Manifold Absolute Pressure
- 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
The PCM adjusts ignition timing based on the following inputs.
- Intake Air Temperature
- Engine Coolant Temperature
- Engine Speed (crankshaft position sensor)
- Knock Sensor
- Manifold Absolute Pressure
- Park/Neutral
- 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 through the same circuit.
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 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 POWERTRAIN DIAGNOSTIC PROCEDURES article and the DRBIII® scan tool.