Operation - Pcm

1. Also refer to Modes of 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 Powertrain Control Module (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 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.

1. A/C request
2. Auto shutdown (ASD) sense
3. Battery temperature
4. Battery voltage
5. Brake switch
6. J1850 bus circuits
7. Camshaft position sensor signal
8. Crankshaft position sensor
9. Data link connections for DRB scan tool
10. Engine coolant temperature sensor
11. Five volts (primary)
12. Five volts (secondary)
13. Fuel level
14. Generator (battery voltage) output
15. Ignition circuit sense (ignition switch in on/off/crank/run position)
16. Intake manifold air temperature sensor
17. Leak detection pump (switch) sense (if equipped)
18. Manifold absolute pressure (MAP) sensor
19. Oil pressure
20. Overdrive/override switch
21. Oxygen sensors
22. Park/neutral switch (auto. trans. only)
23. Power ground
24. Sensor return
25. Signal ground
26. Speed control multiplexed single wire input
27. Throttle position sensor
28. Transmission governor pressure sensor
29. Transmission temperature sensor
30. Vehicle speed (from ABS module)

1. A/C clutch relay
2. Auto shutdown (ASD) relay
3. J1850 (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge and speed control warn. lamp
4. Data link connection for DRBIII(R) scan tool
5. EGR valve control solenoid (if equipped)
6. EVAP canister purge solenoid
7. Fuel injectors
8. Fuel pump relay
9. Generator field driver (-)
10. Generator field driver (+)
11. Generator lamp (if equipped)
12. Idle air control (IAC) motor
13. Ignition coil
14. Leak detection pump
15. Malfunction indicator lamp (Check engine lamp). Driven through J1850 circuits.
16. Overdrive indicator lamp (if equipped). Driven through J1850 circuits.
17. Oxygen sensor heater relays (if equipped).
18. Radiator cooling fan relay (pulse width modulated)
19. Speed control source
20. Speed control vacuum solenoid
21. Speed control vent solenoid
22. Tachometer (if equipped). Driven through J1850 circuits.
23. Transmission convertor clutch circuit
24. Transmission 3-4 shift solenoid
25. Transmission relay
26. Transmission temperature lamp (if equipped)
27. Transmission variable force solenoid