- Preliminary Inspection

BASIC KNOWLEDGE AND TOOLS
To use the Powertrain Management section most effectively, a general understanding of basic electrical circuits and circuit testing tools is required. You should be familiar with wiring diagrams, the meaning of voltage, ohms, amps, the basic theories of electricity, and understand what happens in an open or shorted wire.

To perform system diagnosis, the use of a Tech 1 Diagnostic Computer or equivalent scan tool is required. A test light, ohmmeter, digital voltmeter with 10 megohms impedance, vacuum gauge, and jumper wires are also required. Become acquainted with the special tools and their use before attempting to diagnose a vehicle. Special tools which are required for system service are illustrated in Tools and Equipment.

VISUAL / PHYSICAL UNDERHOOD INSPECTION
A careful visual and physical underhood inspection must be performed as art of any diagnostic procedure or in finding the cause of emissions test failure. This can often lead to fixing a problem without further steps. Inspect all vacuum hoses for correct routing, pinches, cuts, or disconnects. Be sure to inspect hoses that are difficult to see beneath the air cleaner, compressor, generator, etc. Inspect all the wires in the engine compartment for proper connections, burned or chafed spots, pinched wires, or contact with sharp edges or hot exhaust manifolds. This visual / physical inspection is very portant. It must be done carefully and thoroughly.

DIAGNOSTIC INFORMATION
After the visual / physical underhood inspection. The On-Board Diagnostic (OBD) system check is the starting point for all diagnostic procedures and for locating the cause of an emissions test failure.
The correct procedure to diagnose a fault is to follow three basic steps.

1. Are the on-board diagnostics working?
This is determined by performing the On-Board Diagnostic (OBD) system check. This is the starting point for the diagnostic procedures and for finding the cause of an emissions test failure. If the on-board diagnostics are not working, the On-Board Diagnostic (OBD) system check will lead to diagnostic charts in Computers and Control Systems / System Diagnosis. If the on-board diagnostics are working properly, the next step will be:

2. Is there a Diagnostic Trouble Code (DTC) stored?
If a DTC is stored, go directly to the numbered DTC chart in Computers and Control Systems / System Diagnosis. This will determine if the fault is still present. If no DTC is stored, the next step will be:

3. Scan tool serial data transmitted by the control module.
This involves displaying the information available on the serial data stream with a Tech 1 or one of the tools available for that purpose. Information on the meaning of the various displays and examples of normal readings can be found in Computers and Control Systems / System Diagnosis / Scan Tool Diagnosis. Scan Tool Testing and Procedures

TOOLS NEEDED TO SERVICE THE SYSTEM
The system requires a Tech 1, test light, digital multimeter with 10 megohms impedance J 39200, vacuum gage and jumper wires for diagnosis. A test light or voltmeter must be used when specified in the procedures.
For more complete information on the operation of these tools, consult the tool manufacturer's instructions.

VERIFYING VEHICLE REPAIR
Verification of the vehicle repair will be more comprehensive for the vehicles with the OBD II system diagnostics. Following a repair, the technician should perform the following steps:

1. Review the fail records and the freeze frame data for the DTC which was diagnosed. Record the fail records or freeze frame data. The freeze frame data will only store for an A or B type diagnostic and only if the MIL has illuminated.
2. Clear the DTCs.
3. Operate the vehicle within the conditions noted in the fail records or the freeze frame data.
4. Monitor the DTC status information for the specific DTC which has been diagnosed until the diagnostic test associated with that DTC runs.

Following these steps is very important in verifying the repairs on the OBD II systems. Failure to follow these steps could result in unnecessary repair.

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.

NOTE: Do not add on any Add-On vacuum operated equipment to this vehicle. Connect the Add-On electrical operated equipment to the vehicle's electrical system at the battery (power and ground).

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.