System Operation

Diesel fuel injection system components, except for the intake manifold air heater elements, are not directly regulated by the PCM.

Components not operated or regulated by the PCM:
- Fuel tank
- Fuel tank module
- Low and high-pressure fuel supply lines
- Low-pressure, mechanical, fuel transfer pump (fuel lift pump)
- High-pressure fuel injection pump
- Fuel filter/water separator
- Fuel heater
- Fuel heater relay
- Fuel shutdown solenoid
- Fuel shutdown solenoid relay
- High-pressure fuel injectors
- Fuel return line
- Fuel filter (strainer)
- Fuel drain manifold

The powertrain control module (PCM) is located in the right-rear side of the engine compartment (Fig. 1). It is mounted to the dash panel cowl with three bolts. The PCM was formerly referred to as the SBEC or engine controller. Except for operation of the intake manifold air heater elements, the PCM does not regulate or control fuel system operation on the diesel engine.

The 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
- Certain transmission shift features
- ASD relay
- Air conditioning operation
- Tachometer
- Intake manifold air heater

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.

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
- Data link connection for DRB scan tool
- Engine coolant temperature sensor (with EGR system)
- Engine speed sensor (rpm)
- Five volt sensor supply (primary)
- Five volt sensor supply (secondary)
- Generator output
- Intake manifold air temperature sensor
- Oil pressure
- Output shaft speed sensor
- Overdrive/override switch
- Park/neutral switch (auto. trans. only)
- Power ground
- Sensor return
- Signal ground
- Speed control resume switch
- Speed control set switch
- Speed control on/off switch
- Throttle position sensor
- Transmission governor pressure sensor
- Transmission temperature sensor
- Water-in-fuel sensor
- Vehicle speed sensor

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:

PCM Outputs:
- A/C clutch relay
- Auto shutdown (ASD) relay
- CCD bus (+) circuits (if equipped)
- CCD bus (-) circuits (if equipped)
- Data link connection for DRB scan tool
- EGR valve control solenoid (if equipped)
- Generator field driver (-)
- Generator field driver (+)
- Generator lamp (if equipped)
- Malfunction indicator lamp (Check engine lamp)
- Overdrive warning lamp (if equipped)
- Speed control vacuum solenoid
- Speed control vent solenoid
- Tachometer (if equipped)
- Transmission convertor clutch circuit
- Transmission 3-4 shift solenoid
- Transmission relay
- Transmission temperature lamp (if equipped)
- Transmission variable force solenoid (governor sol.)
- Wait-to-start lamp
- Water-in-fuel lamp
- Intake Manifold Air Heater Element #1
- Intake Manifold Air Heater Element #2