PCM Operation - General Info
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PCM operation

    The PCM is a pre-programmed dual microprocessor ditital computer, which monitors various input signals from engine sensors, and then feeds its response to the engine control devices.  The PCM operates in two modes: Open Loop and Closed Loop.  Ignition timing and ignition coil dwell are adjusted in response to engine rpm, manifold absolute pressure, engine coolant temperature, throttle position, transmission gear, vehicle speed, and the brake switch. The PCM also controls the battery charge rate and the AC clutch, and provides speed control operation.

    The fuel injection has these operating modes:

PCM Inputs PCM Outputs
  • Generator output
  • A/C request
  • A/C select
  • Auto shutdown (ASD) sensor
  • Intake manifold air temperature
  • Battery voltage
  • Brake switch
  • Engine coolant temperature
  • Crankshaft position
  • Ignition switch RUN position
  • Manifold Absolute Pressure (MAP)
  • Overdrive/Override switch
  • Oxygen sensors
  • Park/neutral switch
  • SCI receive (DRB scan tool connection)
  • Speed control resume switches
    • set, resume, on/off
  • Camshaft position
  • Throttle position (TPS)
  • Vehicle speed sensor
  • Sensor return
  • power ground
  • Signal ground
  • A/C clutch relay
  • Idle Air Controller (IAC) motor
  • Auto Shutdown (ASD) relay
  • Generator field
  • Malfunction indicator (check engine lamp)
  • EGR valve control solenoid
  • Fuel injectors
  • Fuel pump relay
  • Ignition coils
  • EVAP canister purge solenoid
  • SCI transmit (DRB scan tool connection)
  • Speed control vacuum solenoid
  • Speed control vent solenoid
  • Tachometer

The PCM also contains two 5 volt regulators
to power sensors.

There are several families of PCM's that were developed to meet EPA regulations. These various versions are not interchangeable.




Last update: June 19, 2001