The control module system has a computer, Powertrain Control Module (PCM) to control 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:
| • | Fuel control |
| • | Fuel injection timing |
| • | Transmission shift and shift quality functions |
| • | Specific transmission control diagnostics are covered in the appropriate service manual. |
The diesel Powertrain Control Module (PCM) is located in the passenger compartment and is the control center of the control module system. The PCM used on the electronic fuel injected 6.5L diesel is referred to as PCM.
The PCM constantly looks at the information from various sensors, and controls the systems that affect vehicle performance. The PCM performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the MIL (Service Engine Soon), and store one or more DTCs which identify the problem areas to aid the technician in making repairs. See diagnosis Section for more information.
The PCM is designed to process the various input information and then sends the necessary electrical responses to control fuel delivery, timing and other emission control systems. The input information has an interrelation to more than one output, therefore, if the one input failed it could effect more than one systems operation.
Aftermarket (Add-On) Electrical And Vacuum Equipment
Aftermarket (Add-On) Electrical and Vacuum Equipment is defined as any equipment installed on a vehicle after leaving the factory that connects to the vehicle's electrical or vacuum systems. 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 to these 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.
Electrostatic Discharge Damage
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 are often designed in order to carry very low voltage. 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.
Engine Controls Information
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):
| • | Component Locations |
| • | Wiring Diagrams |
| • | Control Module Terminal End View and Terminal Definitions |
| • | OnBoard Diagnostic (OBD) System Check |
| • | Diagnostic Trouble Code Tables (DTCs) |
The Component System includes the following items:
| • | Component and circuit description |
| • | On-vehicle service for each sub-system |
| • | Functional checks and Diagnostic Tables |
| • | How To Use Electrical Systems Diagnostic Information |
The DTCs also contain diagnostic support information containing circuit diagrams, circuit or system information, and helpful diagnostic information.
Maintenance Schedule
Refer to the General Motors Maintenance Schedule in Section 0B of the appropriate service manual for the maintenance that the owner or the technician should perform in order to retain the emission control performance.
Visual and Physical Underhood Inspection
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:
| • | Inspect all of the vacuum hoses for the following conditions: |
| - | Correct routing |
| - | Pinches |
| - | Cuts |
| - | Disconnects |
| • | Inspect the hoses that are difficult to see beneath the air cleaner, the A/C compressor, the generator, etc. |
| • | Inspect all of the wires in the engine compartment for the following items: |
| - | Proper connections |
| - | Burned or chafed spots |
| - | Pinched wires |
| - | Contact with sharp edges |
| - | Contact with hot exhaust manifolds |
This visual and physical inspection is very important. Preform the inspection carefully and thoroughly.
Basic Knowledge Of Tools Required
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.
Wiring Harness Service
The control module harness electrically connects the control module to the various solenoids, switches, and sensors in the vehicle engine room and the passenger compartment.
Replace the wire harnesses with the proper part number replacement. When splicing the signal wires into a harness, use the 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.
Connectors and Terminals
In order to prevent a shorting between the opposite terminals, use care when probing a connector and when the 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-A , or the equivalent, contains an assortment of flexible connectors that are used in order to probe the terminals during diagnosis. The fuse remover and the test tool BT-8616, or the equivalent, is used for removing a fuse and to adapt the fuse holder to a meter for a diagnosis.
Open circuits are often difficult to locate by sight because of oxidation or terminal misalignment which are hidden by the connectors. Merely wiggling a connector on a sensor, or in the wiring harness may temporarily correct the 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.
