Powertrain Control Module

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. See INPUT DEVICES  , PCM Inputs:

• Ignition Sense
• Battery Voltage
• Brake Switch
• Camshaft Position Sensor
• Intake Air Temperature Sensor
• Crankshaft Position Sensor
• Engine Coolant Temperature (ECT) Sensor
• Manifold Absolute Pressure (MAP) Sensor
• Exhoust Gas: Heated Oxygen Sensors
• SCI Receive
• Throttle Position (TPS) Sensor
• Vehicle Speed Sensor (VSS)
• Air Conditioning Circuit
• ASD Sense Circuit
• Clutch Pedal Position Switch
• MUX Circuit
• Sense Return
• CCD To Security System

Based on these inputs, the PCM adjusts various engine and vehicle operations through devices referred to as Powertrain Control Module Outputs. See OUTPUT SIGNALS  , PCM Outputs:

• Air Conditioning Clutch Relay
• Idle Air Control (IAC) Motor
• Auto Shutdown (ASD) & Fuel Pump Relays
• Malfunction Indicator (Check Engine) Lamp
• Self Diagnostic System
• EVAP Canister Purge Solenoid
• Fuel Injectors
• Radiator Fan On Relay
• Radiator Fan High/Low Speed Relay
• Tachometer
• Skip Shift Solenoid
• Reverse Lockout Solenoid
• SCI Transmit
• First To Fourth Gear Shift Lamp
• Cooling Fan Motor
• Fuel Control
• Ignition Control
• Fuel Pressure Regulator

The PCM has several Modes Of Operation. See MODES OF OPERATION . The Modes consist of

• Ignition Switch On (Zero RPM) Mode
• Engine Start-Up Mode
• Engine Warm-Up Mode
• Cruise And Idle Mode
• Acceleration Mode
• Deceleration Mode
• Wide Open Throttle Mode
• Ignition Switch Off Mode

Based on inputs it receives, the PCM adjusts fuel injector pulse width, idle speed, and canister purge operation. The PCM also regulates the cooling fan, and air conditioning.

The PCM adjusts injector, pulse width (air/fuel ratio) based on the following inputs:

• Battery Voltage
• Intake Air Temperature
• Engine Coolant Temperature
• Exhaust Gas Oxygen Content (Heated Oxygen Sensors)
• 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:

• Engine Coolant Temperature
• Engine Speed (Crankshaft Position Sensor)
• Manifold Absolute Pressure
• Throttle Position
• Time Delay After Start-Up

The auto shutdown (ASD) and fuel pump relays are mounted externally, but are turned on and off by the PCM through the same circuit.

The camshaft position sensor and crankshaft position sensor signals are sent to the PCM. 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 contains a voltage converter that changes battery voltage to a regulated 8.0 volts. The 8.0 volts power the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5.0 volts supply for the engine coolant temperature sensor, intake air temperature sensor, manifold absolute pressure sensor and throttle position sensor.