Powertrain Control Module: Description: Description
The Powertrain Control Module (PCM) is a digital computer containing a microprocessor (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, transmission, and vehicle operations through devices referred to as Powertrain Control Module Outputs.
- Air Conditioning Pressure Transducer
- ASD Relay
- Battery Voltage
- Brake Switch Status
- Camshaft Position Sensor
- Crankshaft Position Sensor
- Distance Sensor
- EGR Position Feedback
- Engine Coolant Temperature Sensor
- Heated Oxygen Sensors
- Ignition sense
- Intake Air Temperature Sensor
- Knock Sensor
- Manifold Absolute Pressure (MAP) Sensor
- Natural Vacuum Leak Detection
- PCI Bus
- Power Steering Pressure Switch
- Proportional Purge Sense
- SCI Receive
- Speed Control
- Throttle Position Sensor
- Torque Management Input (Integral to PCM)
- Transmission Control Relay (Switched B+)
- Transmission Range Sensor (TRS)
- Transmission Pressure Switches (L/R, 2/4, OD)
- Transmission Temperature Sensor (Integral to TRS).
- Transmission Input Shaft Speed Sensor
- Transmission Output Shaft Speed Sensor
- TRS Hall Effect Switch (Autostick)
- Vehicle Speed (From Transmission)
- 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
- Low Speed Fan Relay
- MTV Actuator
- Natural Vacuum Leak Detection
- Proportional Purge Solenoid
- SRV Valve
- Speed Control Relay
- Speed Control Vent Relay
- Speed Control Vacuum Relay
- Transmission Autostick Display (To Cluster)
- Transmission Control Relay
- Transmission PRNDL Position (To Cluster)
- Transmission Solenoids (L/R, 2/4, OD and UD)
- Transmission Torque Reduction Request (Internal to PCM)
- Transmission Temperature (Internal to PCM)
- Vehicle Speed (Internal to PCM)
- 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. The PCM also determines the appropriate transmission shift schedule and shift points, depending on the present operating conditions and driver demand. 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
- EGR valve position (if equipped)
- Engine Coolant Temperature
- Engine Speed (crankshaft position sensor)
- EVAP Purge Valve Position
- 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 (transmission gear selection)
- Transaxle Gear Engagement
- Throttle Position
- Vehicle Speed (from Transmission)
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 (transmission gear selection)
- Transaxle Gear Engagement
- Throttle Position
In addition to monitoring inputs and controlling outputs, the PCM has other important transmission related responsibilities and functions:
- Storing and maintaining Clutch Volume Indices (CVI)
- Storing and selecting appropriate Shift Schedules
- System self-diagnostics
- Diagnostic capabilities (with DRB III scan tool)
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 two 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 5.0 volts. The 5.0 volts power the camshaft position sensor, crankshaft position sensor, vehicle speed sensor, engine coolant temperature sensor, intake air temperature sensor, manifold absolute pressure sensor, and throttle position 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 DRB scan tool to change the mileage in the PCM. Refer to the POWERTRAIN DIAGNOSTIC PROCEDURES and the DRB scan tool .