Powertrain Control Module: Operation: Operation
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 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 Inputs:
- A/C Pressure Transducer
- Air Conditioning Controls
- ASD Sense
- Battery Temperature
- Battery voltage
- Brake Switch
- Camshaft Position Sensor
- Crankshaft Position Sensor
- Engine Coolant Temperature Sensor
- Ignition Switch
- Intake Air Temperature Sensor
- J1850 Bus
- Leak Detection Pump Switch
- Manifold Absolute Pressure (MAP) Sensor
- Oil Pressure Sensor
- Oil Temperature Transducer
- Oxygen Sensors
- SCI Receive
- Throttle Position Sensor
- Vehicle Speed Sensor
PCM Outputs:
- Air Conditioning Clutch Relay
- Auto Shutdown (ASD) Relay
- Data Link Connector
- Duty Cycle EVAP Canister Purge Solenoid
- Double Start Override Relay
- Downstream O2 Heater Relay
- Fuel Injectors
- Fuel Pump Relay
- Generator Field Ground Control
- Hydraulic Fan Solenoid Control
- Idle Air Control Motor
- Ignition Coils
- J1850 Bus
- SCI Transmit
- Reverse Gear Lockout Solenoid
- Upstream O2 Heater Control
- 2nd/3rd Gear Lockout Solenoid
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, and air conditioning. 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
- Intake air temperature
- Exhaust gas content (oxygen sensor)
- Engine speed (crankshaft position sensor)
- Manifold absolute pressure
- Throttle position
The PCM adjusts ignition timing based on the following inputs.
- Coolant temperature
- Intake air temperature
- Engine speed (crankshaft position sensor)
- Manifold absolute pressure
- Throttle position
The PCM also adjusts engine idle speed through the idle air control motor based on the following inputs.
- Air conditioning sense
- Battery voltage
- Coolant temperature
- Engine speed (crankshaft position sensor)
- Engine run time
- Manifold absolute pressure
- Throttle position
- Vehicle distance (speed)
The Auto Shutdown (ASD) and fuel pump relays are mounted externally, but turned on and off by the PCM.
The crankshaft position sensor signal is sent to the PCM. If the PCM does not receive the signal within approximately one second of engine cranking, it deactivates the ASD relay and fuel pump relay. When these relays deactivate, power is shut off the fuel injectors, ignition coils, heating element in the upstream oxygen sensors, hydraulic fan solenoid and the 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 and vehicle speed sensor. The PCM also provides a 5 volt direct current supply for the manifold absolute pressure sensor and throttle position sensor.