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Powertrain Control Module: Operation: Notes

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, speed control (if equipped), 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 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 (2.5L only), 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 the 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.

NOTE: Powertrain Control Module (PCM) Inputs:
  1. A/C request (if equipped with factory A/C)
  2. A/C select (if equipped with factory A/C)
  3. Auto shutdown (ASD) sense
  4. Battery temperature
  5. Battery voltage
  6. Brake switch
  7. CCD bus (+) circuits
  8. CCD bus (-) circuits
  9. Camshaft position sensor signal
  10. Crankshaft position sensor
  11. Data link connector for DRB scan tool
  12. Engine coolant temperature sensor
  13. Fuel level
  14. Generator (battery voltage) output
  15. Ignition circuit sense (ignition switch in run position)
  16. Intake manifold air temperature sensor
  17. Leak detection pump (if equipped)
  18. Manifold Absolute Pressure (MAP) sensor
  19. Oil pressure sensor
  20. Oxygen sensors
  21. Park/neutral switch (auto. trans. only)
  22. Power ground
  23. Power steering pressure switch (2.5L only)
  24. SCI receive (DRB scan tool 16-way connection)
  25. Sensor return
  26. Signal ground
  27. Speed control multiplexed single wire input
  28. Throttle position sensor
  29. Vehicle speed sensor
NOTE: Powertrain Control Module (PCM) Outputs:
  1. A/C clutch relay
  2. Auto Shutdown (ASD) relay
  3. CCD bus (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge and speed control warn. lamp
  4. Duty cycle EVAP canister purge solenoid
  5. Five volt sensor supply (primary)
  6. Five volt sensor supply (secondary)
  7. Fuel injectors
  8. Fuel pump relay
  9. Generator field driver (-)
  10. Generator field source (+)
  11. Idle Air Control (IAC) motor
  12. Ignition coil
  13. Leak detection pump (if equipped)
  14. Malfunction indicator lamp (Check engine lamp). Driven through CCD circuits.
  15. SCI transmit (DRB scan tool 16-way connection)
  16. Speed control vacuum solenoid
  17. Speed control vent solenoid
  18. Tachometer (if equipped). Driven through CCD circuits.
  19. Transmission convertor clutch solenoid
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