Powertrain Control Module: Operation
The PCM operates the fuel system. The PCM is a pre-programmed, triple microprocessor digital computer. It regulates ignition timing, air/fuel ratio, emission control devices, charging system, certain transmission features, speed control, air conditioning compressor clutch engagement and idle speed. The PCM can adapt its programming to meet changing operating conditions. The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM regulates various engine and vehicle operations through different system components. These components are referred to as Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs to the PCM are considered PCM Inputs.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to engine RPM, manifold absolute pressure, engine coolant temperature, throttle position, transmission gear selection (automatic transmission), vehicle speed, power steering pump pressure, and the brake switch. The PCM adjusts idle speed based on inputs it receives from sensors that react to throttle position, vehicle speed, transmission gear selection, engine coolant temperature and from inputs it receives from air conditioning clutch switch and brake switch. Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator charge rate through control of the generator field and provides speed control operation.
The following inputs may be used may be used by the PCM.
- A/C Request (If Equipped With Factory A/C)
- A/C Select (If Equipped With Factory A/C)
- Auto Shutdown Sense
- Battery Temperature
- Battery Voltage
- Brake Switch
- CCD Bus (+) Circuits
- CCD Bus (-) Circuits
- Camshaft Position Sensor
- Crankshaft Position Sensor
- Data Link Connector For DRBIII(R)
- Engine Coolant Temperature Sensor
- Fuel Level
- Generator (Battery Voltage) Output
- Ignition Circuit Sense (Ignition Switch In Run Position)
- Intake Air Temperature Sensor
- Leak Detection Pump
- Manifold Absolute Pressure Sensor
- Oil Pressure Sensor
- Oxygen Sensors
- Park/Neutral Switch (A/T Only)
- Starter Relay
- Power Ground
- Power Steering Pressure Switch (If Equipped)
- SCI Receive (DRBIII(R) 16-Pin Data Link Connection)
- Sensor Return
- Signal Ground
- Speed Control Multiplexed Single Wire Input
- Throttle Position Sensor
- Transfer Case Switch (4WD Range Position), If Equipped
- Vehicle Speed Sensor
The following outputs are controlled by the PCM.
- A/C Clutch Relay
- Auto Shutdown Relay
- J1850 Bus (+/-) Circuits For Speedometer, Voltmeter, Fuel Gauge, Oil Pressure Gauge/Light, Engine Temperature Gauge & Speed Control Warning Light
- Clutch Pedal Position Switch Override Relay
- Data Link Connection For DRBIII(R)
- EGR Solenoid (If Equipped)
- EVAP Canister Purge Solenoid
- 5-Volt Sensor Supply (Primary)
- 5-Volt Sensor Supply (Secondary)
- Fuel Injectors
- Fuel Pump Relay
- Generator Field Driver (-)
- Generator Field Driver (+)
- Idle Air Control Motor
- Ignition Coil(s)
- Leak Detection Pump
- Malfunction Indicator Light
- Ignition Circuit Sense (Ignition Switch In Run Position)
- Oxygen Sensor Heater Relay
- Oxygen Sensors (Pulse Width Modulated)
- Radiator Cooling Fan Relay (If Equipped)
- Speed Control Vacuum Solenoid
- Speed Control Vent Solenoid
- Tachometer (If Equipped)
- Transmission Converter Clutch Solenoid
- Transmission 3-4 Shift Solenoid (Grand Cherokee)
- Transmission Relay (Grand Cherokee)
- Transmission Temperature Light, If Equipped (Grand Cherokee)
- Transmission Variable Force Solenoid (Grand Cherokee)
- Power Steering Pressure Switch (If Equipped)
- SCI Receive (DRBIII(R) 16-Pin Connection)
- Sensor Return
- Signal Ground
- Speed Control Multiplexed Single Wire Input
- Throttle Position Sensor
- Transfer Case Switch (4WD Range Position)
- Vehicle Speed Sensor