General System Description

System Schematic:

DESCRIPTION
The Powertrain Control Module (PCM) is a pre-programmed, dual micro-processor digital computer. Although it does not regulate or control the fuel system on the diesel powered engine, it does operate or regulate the:

- Speed control system
- Charging system
- Certain warning lamps
- Transmission overdrive solenoid
- Torque convertor engagement
- ASD relay
- Air conditioning operation
- Tachometer
- Intake manifold air heater

The PCM can adapt its programming to meet changing operating conditions.

PCM Inputs
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.

Air conditioning selection
Battery voltage
Brake light switch
Engine speed sensor (RPM)
Speed control switch position
Auto shut down (ASD) sense
Battery voltage input used to measure generator output
Intake manifold air temperature sensor
Overdrive/override switch
Park/neutral switch (auto. trans. only)
Power ground
SCI receive (DRB scan tool connection)
Sensor return
Throttle position sensor (auto. trans. only)
Transmission temperature sensor (auto. trans. only)
Vehicle speed sensor
Water-in-fuel sensor
Ignition switch sense

PCM Outputs
After inputs are received by the PCM, certain sensors, switches and components are controlled or regulated by the PCM. These are considered PCM Outputs. These outputs are for:

A/C clutch relay (A/C clutch operation)
Auto shut down (ASD) relay
Data link connectors (for DRB and MDS test equipment)
Generator field (charging system operation)
Malfunction indicator lamp (Check Engine Lamp)
Overdrive solenoid electrical operation (auto. trans. only)
Overdrive/Override warning lamp (auto. trans. only)
SCI transmit (DRB scan tool connection)
Speed control vacuum solenoid
Speed control vent solenoid
Tachometer
Torque convertor electrical operation (auto. trans. only)
Transmission oil temperature warning lamp (auto. trans. only)
Wait-to-start lamp
Water-in-fuel lamp
Intake manifold air heater #1
Intake manifold air heater #2