Powertrain Control Module: Notes
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, transmission, and vehicle operations through devices that are referred to as PCM Outputs. See Fig 1.
- Air Conditioning Controls
- Ambient Air temperature Sensor
- ASD Sense
- Baro/Tip (Turbo)
- Battery Voltage
- Battery Temperature Sensor
- Brake Switch
- Camshaft Position Sensor
- Clutch Upstop Switch
- Clutch Interlock
- Crankshaft Position Sensor
- Engine Coolant Temperature Sensor
- Fuel Level Sensor (Bus message)
- Ignition Switch
- Intake Air Temperature Sensor
- J1850 (1.6L)
- CAN C Bus (2.4L)
- Knock Sensor (2.4L)
- Natural Vacuum Leak Detection (NVLD)
- Manifold Absolute Pressure (MAP) Sensor
- Oil Pressure Switch
- Oxygen Sensors
- Power Steering Pressure Switch
- Speed Control Switches
- Throttle Position Sensor
- Transmission Control Relay (Switched B+)
- Transmission Input Shaft Speed Sensor
- Transmission Output Shaft Speed Sensor
- Transmission Pressure Switches (L/R, 2/4, OD)
- Transmission Range Sensor (TRS)
- Transmission Oil Temperature Sensor (Integral to TRS)
- Vehicle Speed Sensor (MTX-equipped models)
- Air Conditioning Clutch Relay
- Auto Shutdown (ASD) Relay
- Charging Indicator Lamp (Bus Message)
- Proportional Purge Solenoid
- EGR Solenoid
- Fuel Injectors
- Fuel Pump Relay
- Generator Field
- Idle Air Control Motor (2.4L)
- Ignition Coils
- J1850 (1.6L)
- CAN C Bus (2.4L)
- Malfunction Indicator (Check Engine) Lamp (Bus Message)
- Oxygen Sensors Heater Controls
- Radiator Fan Relays
- Speed Control Solenoids (2.4L)
- Transmission Control Relay
- Transmission Solenoids (LR/CC, 2/4, OD, and UD)
- Transmission PRNDL Position (to Cluster)
- Transmission Torque Reduction Request (Internal to PCM)
- Transmission Temperature (Internal to PCM and a Bus Message)
- Vehicle Speed (Manual Transmission)
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 also determines the appropriate transmission shift schedule and shift points, depending on the present operating conditions and driver demand. 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.
- Battery voltage
- Coolant temperature
- Exhaust gas content (oxygen sensor)
- Engine speed (crankshaft position sensor)
- Intake air temperature
- Manifold absolute pressure
- Throttle position
The PCM adjusts ignition timing based on the following inputs.
- Coolant temperature
- Engine speed (crankshaft position sensor)
- Knock sensor
- Manifold absolute pressure
- Throttle position
- Transmission gear selection (park/neutral switch)
- Intake air temperature
The PCM also adjusts engine idle speed through the idle air control motor based on the following inputs.
- Air conditioning sense
- Battery voltage
- Battery temperature
- Brake switch
- Coolant temperature
- Engine speed (crankshaft position sensor)
- Engine run time
- Manifold absolute pressure
- Power steering pressure switch
- Throttle position
- Transmission gear selection (park/neutral switch)
- Vehicle distance (speed)
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 control. When the relay/control is 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 5 volts direct current to power the camshaft position sensor, crankshaft position sensor, manifold absolute pressure sensor, throttle position sensor, A/C pressure switch, A/C pressure transducer, and vehicle speed sensor.