OPERATION

POWERTRAIN CONTROL MODULE (PCM)

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 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.

NOTE: PCM Inputs:

• Accelerator pedal position sensor (if equipped)
• A/C request (if equipped with factory A/C)
• A/C select (if equipped with factory A/C)
• Auto shutdown (ASD) sense
• Battery temperature
• Battery voltage
• Brake switch
• CAN bus (+) circuits
• CAN bus (-) circuits
• Camshaft position sensor signal
• Clutch Interlock Switch (if equipped)
• Crankshaft position sensor
• Data link connection for diagnostic scan tool
• EGR position sensor (if equipped)
• Engine coolant temperature sensor
• Fuel level
• Generator (battery voltage) output
• Ignition circuit sense (ignition switch in on/off/crank/run position)
• Intake manifold air temperature sensor
• Knock sensor(s) (if equipped)
• Leak detection pump (switch) sense (if equipped)
• Manifold absolute pressure (MAP) sensor
• Oil pressure sensor
• Output shaft speed sensor
• Overdrive/override switch
• Oxygen sensors
• Park/neutral switch (auto. trans. only)
• Power ground
• Power steering pressure switch (if equipped)
• Sensor return
• Signal ground
• Speed control multiplexed single wire input
• Throttle position sensor
• Transmission governor pressure sensor
• Transmission output speed sensor
• Transmission temperature sensor
• Vehicle speed inputs from ABS or RWAL system

NOTE: PCM Outputs:

• A/C 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 (if equipped)
• Speed control vacuum solenoid
• Speed control vent solenoid
• Starter relay
• Tachometer (if equipped). Driven through CAN bus circuits.
• Transmission convertor clutch circuit
• Transmission 3-4 shift solenoid
• Transmission relay
• Transmission temperature lamp (if equipped)
• Transmission variable force solenoid

5 VOLT SUPPLIES

Primary 5–volt supply:

• supplies the required 5 volt power source to the Crankshaft Position (CKP) sensor.
• supplies the required 5 volt power source to the Camshaft Position (CMP) sensor.
• supplies a reference voltage for the Manifold Absolute Pressure (MAP) sensor.
• supplies a reference voltage for the Throttle Position Sensor (TPS) sensor.

Secondary 5–volt supply:

• supplies the required 5 volt power source to the oil pressure sensor.
• supplies the required 5 volt power source for the Vehicle Speed Sensor (VSS) (if equipped).
• supplies the 5 volt power source to the transmission pressure sensor (if equipped with an RE automatic transmission).

IGNITION CIRCUIT SENSE

The ignition circuit sense input tells the PCM the ignition switch has energized the ignition circuit.

Battery voltage is also supplied to the PCM through the ignition switch when the ignition is in the RUN or START position. This is referred to as the "ignition sense" circuit and is used to "wake up" the PCM. Voltage on the ignition input can be as low as 6 volts and the PCM will still function. Voltage is supplied to this circuit to power the PCM's 8-volt regulator and to allow the PCM to perform fuel, ignition and emissions control functions.