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Home >> Isuzu Truck >> 1998 >> Hombre XS Regular Cab 2WD L4-2.2L CPC >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Engine Control Module >> Description and Operation >> Powertrain Control Module Description Part 1

Powertrain Control Module Description Part 1

The Control Module refers to the Powertrain Control Module (PCM) and the Vehicle Control Module (VCM). The control module is designed to maintain exhaust emission levels to Federal or California standards while providing excellent driveability and fuel efficiency. Review the components and wiring diagrams in order to determine which systems are controlled by each specific control module. The control module monitors numerous engine and vehicle functions. The control module controls the following operations:
- Fuel control
- Ignition Control (IC)
- Knock Sensor (KS) system
- Automatic transmission shift functions
- Cruise Control Enable
- Generator
- Evaporative Emission (EVAP) Purge
- A/C Clutch Control
- Cooling Fan Control

Control Module Function
The Control Module supplies a buffered voltage to various sensors and switches. The input and output devices in the control module include an analog to digital converters, signal buffers, counters, and special drivers. The Control Module controls most components with electronic switches which complete a ground circuit when turned ON. These switches are arranged in groups of 4 and 7 called one of the following:
- Quad Driver Module
- Output Driver Modules
The surface mounted Quad Driver Module can independently control up to 4 outputs (Control Module) terminals. The Output Driver Modules can independently control up to 7 outputs. Not all outputs are always used.

Use of Circuit Testing Tools
Do not use a test lamp in order to diagnose the Powertrain electrical Systems unless specifically instructed by the diagnostic procedures. Use the Connector Test Adapter Kit, J 35616 whenever the diagnostic procedures call for probing any of the connectors.

Control Module Service Precautions
The control module is designed to withstand the normal current draws that are associated with the vehicle operations. Avoid overloading any circuit. When testing for opens or shorts, do not ground any of the control module circuits unless instructed. When testing for opens or shorts, do not apply voltage to any of the control module circuits unless instructed. Only test these circuits with digital voltmeter J 39200, while the control module connectors remain connected to the control module.

Aftermarket (Add-On) Electrical And Vacuum Equipment
The Aftermarket (Add-On) Electrical and Vacuum Equipment is defined as any equipment installed on a vehicle after leaving the factory that connects to the electrical or vacuum systems of the vehicle. 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.
The Add-On electrical equipment, even when installed to these strict guidelines, may still cause the Powertrain system to malfunction. This may also include any equipment which is not connected to the electrical system of the vehicle such as portable telephones and radios. Therefore, the first step in diagnosing any Powertrain problem is to eliminate all of the 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.


The electronic components used in the control systems are often designed in order to carry very low voltage. The 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 Use care when handling and testing the 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):
- The Component Locations
- The Wiring Diagrams
- The Control Module Terminal End View and Terminal Definitions
- The OnBoard Diagnostic (OBD) System Check
- The Diagnostic Trouble Code Tables (DTCs) The Component System includes the following items:
- The Component and circuit description
- The On-vehicle service for each sub-system
- The Functional checks with the Diagnostic Tables
- How To Use Electrical Systems Diagnostic Information
The DTCs also contain the diagnostic support information containing the circuit diagrams, the circuit or the system information, and helpful diagnostic information.

Maintenance Schedule
Refer to the General Motors Maintenance Schedule in Section OB of the appropriate service manual for the maintenance that the owner or technician should perform in order to retain 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.

System Status and Drive Cycle For Satisfying the Federal Inspection/Maintenance (I/M 240) Regulations
The System Status selection is included in the scan tool System Info menu. Several states require that the I/M 240 (OBD II system) pass on-board tests for the major diagnostics prior to having a vehicle emission inspection. This is also a requirement to renew license plates in some areas.
Using a scan tool, the technician can observe the System Status (complete or not complete) in order to verify that the vehicle meets the criteria which complies with local area requirements. Using the System Status display, any of the following systems or a combination of the systems may be monitored for I/M Readiness:
- The Catalyst
- The HO2S
- The HO2S Heater
- The EGR System
Important: The System Status display indicates only whether or not the test has been completed. The System Status display does not necessarily mean that the test has passed. If a Failed Last Test indication is present for a DTC associated with one of the above systems, that test is failed; diagnosis and repair is necessary in order to meet the I/M 240 requirement. Verify that the vehicle passes all of the diagnostic tests associated with the displayed System Status' prior to returning the vehicle to the customer. Refer to the Typical OBD II Drive Cycle table (more than one drive cycle may be needed) to use as a guide to complete the l/M 240 System Status tests.

Following a DTC info clear, the System Status will clear only for the Systems affected by any DTCs stored. Following a battery disconnect or a Control Module replacement, all of the System Status information will clear.



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