Operation

OPERATION

The PCM is a pre-programmed, 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 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, vehicle speed and the brake switch activation.

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, A/C compressor clutch operation and brake switch activation.

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 cruise control operation.

NOTE: PCM Inputs:

- Accelerator pedal position
- A/C request
- A/C select
- Auto shutdown (ASD)
- Battery temperature
- Battery voltage
- Brake switch
- CAN bus (+) circuits
- CAN bus (-) circuits
- Camshaft position
- Crankshaft position
- Data link connection for diagnostic scan tool
- EGR position (if equipped)
- Engine coolant temperature
- Fuel level
- Generator (battery voltage) output
- Ignition circuit sense (ignition switch in on/off/crank/run position)
- Engine intake air temperature
- Knock sensors
- Leak detection pump (switch) sense (if equipped)
- Manifold absolute pressure (MAP)
- Oil pressure
- Transmission output shaft speed
- Overdrive/override switch
- Oxygen sensors
- Park/neutral switch
- Power ground
- Power steering pressure switch
- Sensor return
- Signal ground
- Speed control switch
- Throttle position sensor
- Transmission governor pressure
- Transmission temperature
- Vehicle speed

NOTE: PCM Outputs:

- A/C compressor clutch relay
- Auto shutdown (ASD) relay
- CAN bus (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge and speed control warn. lamp
- Data link connection for diagnostic scan tool
- Double start override (if equipped)
- EGR valve control solenoid (if equipped)
- Electronic throttle control
- EVAP canister purge solenoid
- Five volt sensor supply (primary)
- Five volt sensor supply (secondary)
- Fuel injectors
- Fuel pump relay
- Generator field driver (-)
- Generator field driver (+)
- Generator lamp (if equipped)
- Idle air control (IAC) motor
- Ignition coil(s)
- CAN bus circuits
- Leak detection pump (if equipped)
- Malfunction indicator lamp (Check engine lamp). Driven through CAN bus circuits.
- Overdrive indicator lamp (if equipped)
- Radiator cooling fan
- Starter relay
- Tachometer (if equipped). Driven through CAN bus circuits.
- Transmission converter clutch circuit
- Transmission 3-4 shift solenoid
- Transmission relay
- Transmission temperature lamp (if equipped)
- Transmission variable force solenoid