Description

Fig. 8 PCM Location:

POWERTRAIN CONTROL MODULE
The Powertrain Control Module (PCM) is located in the engine compartment. The PCM is referred to as JTEC.

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.

NOTE: PCM Inputs:
* 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
* CCD bus (+) circuits
* CCD bus (-) circuits
* Camshaft position sensor signal
* Crankshaft position sensor
* Data link connection for DRB scan tool
* 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
* Leak detection pump (switch) sense (if equipped)
* Manifold Absolute Pressure (MAP) sensor
* Oil pressure
* Output shaft speed sensor
* Overdrive/override switch
* Oxygen sensors
* Park/neutral switch (auto. trans. only)
* Power ground
* Sensor return
* Signal ground
* Speed control multiplexed single wire input
* Throttle position sensor
* Transmission governor pressure sensor
* Transmission temperature sensor
* Vehicle speed inputs from ABS or RWAL system

NOTE: PCM Outputs:
* A/C clutch relay
* Auto Shutdown (ASD) relay
* CCD bus (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge and speed control warn. lamp
* Data link connection for DRB scan tool
* EGR valve control solenoid (if equipped)
* 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
* Leak detection pump (if equipped)
* Malfunction indicator lamp (Check engine lamp). Driven through CCD circuits.
* Overdrive indicator lamp (if equipped)
* Speed control vacuum solenoid
* Speed control vent solenoid
* Tachometer (if equipped). Driven through CCD circuits.
* Transmission convertor clutch circuit
* Transmission 3-4 shift solenoid
* Transmission relay
* Transmission temperature lamp (if equipped)
* Transmission variable force solenoid

5 Volt Supplies
Two different Powertrain Control Module (PCM) five volt supply circuits are used; primary and secondary

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
This circuit ties the ignition switch to the Powertrain Control Module (PCM).

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.

Power Grounds
The Powertrain Control Module (PCM) has 2 main grounds. Both of these grounds are referred to as power grounds. All of the high-current, noisy, electrical devices are connected to these grounds as well as all of the sensor returns. The sensor return comes into the sensor return circuit, passes through noise suppression, and is then connected to the power ground.

The power ground is used to control ground circuits for the following PCM loads:
* Generator field winding
* Fuel injectors
* Ignition coil(s)
* Certain relays/solenoids
* Certain sensors

Sensor Return
The Sensor Return circuits are internal to the Powertrain Control Module (PCM).
Sensor Return provides a low-noise ground reference for all engine control system sensors. Refer to Power Grounds for more information.

Signal Ground
Signal ground provides a low noise ground to the data link connector.