The control module system has a powertrain control module (PCM) that controls fuel delivery, timing, and some emission control systems. The control module system monitors a number of engine and vehicle functions and controls the following operations:

The diesel powertrain control module (PCM) is located in the passenger compartment. The PCM is the control center of the control module system.

The PCM constantly monitors information from various sensors and controls the systems that affect vehicle performance. The PCM performs the diagnostic functions of the system. The PCM can recognize operational problems, alert the driver through the MIL (Service Engine Soon), and store one or more DTCs identifying the problem areas to aid the technician in making repairs. Refer to the Diagnosis Section for more information.

The PCM is designed to process the various input information and send the electrical responses necessary to control fuel delivery, timing, and other emission control systems. The input information has an interrelation to more than one output, therefore, if input from one source failed, more than one system's operations could be affected.

Aftermarket (Add-On) Electrical and Vacuum Equipment is defined as any equipment that connects to a vehicle's electrical or vacuum systems that is installed on a vehicle after the vehicle leaves the factory . No allowances have been made in the vehicle design for this type of equipment.

Notice: Do not attach add-on vacuum operated equipment to this vehicle. The use of add-on vacuum equipment may result in damage to vehicle components or systems.

Notice: Connect any add-on electrically operated equipment to the vehicle's electrical system at the battery (power and ground) in order to prevent damage to the vehicle.

Add-on electrical equipment, even when installed in accordance with strict guidelines, may still cause the powertrain system to malfunction. This may also include equipment not connected to the vehicle's electrical system, such as portable telephones and radios. Therefore, the first step in diagnosing any powertrain problem is to eliminate all aftermarket electrical equipment from the vehicle. After this is done, if the problem still exists, diagnose the problem in the normal manner.

Notice: In order to prevent possible Electrostatic Discharge damage to the PCM, Do Not touch the connector pins or the soldered components on the circuit board.

Electronic components used in the control systems often carry very low voltage. These electronic components are susceptible to damage caused by electrostatic discharge. Less than 100 volts of static electricity can cause damage to some electronic components. There are several ways for a person to become statically charged. The most common methods of charging are by friction and by induction. An example of charging by friction is a person sliding across a car seat. Charging by induction occurs when a person with well insulated shoes stands near a highly charged object and momentarily touches ground. Charges of the same polarity are drained off leaving the person highly charged with the opposite polarity. Static charges can cause damage; therefore, it is important to use care when handling and testing electronic components.

The driveability and emissions information describes the function and operation of the control module. The emphasis is placed on the diagnosis and repair of problems related to the system.

Engine Components, Wiring Diagrams, and Diagnostic Tables (DTCs) include the following items:

The Component System includes the following items:

The DTCs also contain diagnostic support information that includes circuit diagrams, circuit or system information, and helpful diagnostic information.

Refer to the General Motors Maintenance Schedule, Owner Checks and Services in the Maintenance and Lubrication section of the appropriate service manual for maintenance the owner or the technician should perform in order to retain the emission control performance.

Perform a careful visual and physical underhood inspection when performing any diagnostic procedure or diagnosing the cause of an emission test failure. This can often lead to repairing a problem without further steps. Use the following guidelines when performing a visual and physical inspection:

This visual and physical inspection is very important. Perform the inspection carefully and thoroughly.

Notice: Lack of basic knowledge of this powertrain when performing diagnostic procedures could result in incorrect diagnostic performance or damage to powertrain components. Do not attempt to diagnose a powertrain problem without this basic knowledge.

A basic understanding of hand tools is necessary in order to effectively use this information.

The control module harness electrically connects the control module to the various solenoids, switches, and sensors in the vehicle engine compartment and the passenger compartment.

Replace the wire harnesses with the proper part number replacement. When splicing the signal wires into a harness, use wiring that has high-temperature insulation.

Consider the low amperage and voltage levels that are utilized in the powertrain control systems. Make the best possible bond at all of the splices. Use rosin-core solder in these areas.

Molded-on connectors require a complete replacement of the connector. Splice a new connector into the harness. Replacement connectors and terminals are listed in Group 8.965 in the Standard Parts Catalog.

For a wiring repair, refer to Wiring Repairs in Wiring Systems.

In order to prevent shorting between opposite terminals, use care when probing a connector and when replacing terminals. Damage to the components could result.

Always use jumper wires between connectors for circuit checking.

Never probe through Weather-Pack seals.

The connector test adapter kit J 35616 , or the equivalent, contains an assortment of flexible connectors used in order to probe the terminals during diagnosis. The fuse remover and the test tool BT-8616, or the equivalent, are used for fuse removal and for adapting the fuse holder to a meter for diagnosis.

Open circuits are often difficult to locate by sight because of oxidation or terminal misalignment that is hidden by the connectors. Merely wiggling a connector on a sensor, or in the wiring harness, may temporarily correct an open circuit. Oxidized or loose connections may cause intermittent problems.

Be certain of the type of connector and the terminal before making any connector or terminal repair. Weather-Pack and Com-Pack III terminals look similar, but are serviced differently.