- Preliminary Inspection

PCM SERVICE PRECAUTIONS
The control module is designed to withstand normal current draws associated with vehicle operations. Avoid overloading any circuit. When testing for opens or shorts, do not ground or apply voltage to any of the control module circuits unless instructed to do so. These circuits should only be tested using digital voltmeter J 39200, while the control module connectors remain connected to the control module or the recommended breakout box.

BASIC KNOWLEDGE OF TOOLS REQUIRED
A basic understanding of hand tools is necessary to effectively use this section of the Service Manual.

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

USE OF CIRCUIT TESTING TOOLS
Do not use a test light to diagnose the powertrain electrical systems unless specifically instructed by diagnostic procedures. Use Connector Test Adapter Kit, J 35616 whenever diagnostic procedures call for probing any connectors.

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:
- No add-on vacuum equipment should be added to this vehicle.
- Add-on electrical equipment must only be connected to the vehicles 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 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, it may be diagnosed in the normal manner.

VISUAL / 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/physical inspection:

- Inspect all vacuum hoses for correct routing, pinches, cuts, or disconnects.
- Inspect hoses that are difficult to see beneath the air cleaner, A/C compressor, generator, etc.
- Inspect all wires in the engine compartment for proper connections, burned or chafed spots, pinched wires, contact with sharp edges or contact with hot exhaust manifolds.

This visual/physical inspection is very important. It must be done carefully and thoroughly.

DIAGNOSTIC INFORMATION
The diagnostic charts and functional checks are designed to locate a faulty circuit or component through a process of logical decisions. The diagnostic charts are prepared with the requirement that the vehicle functioned correctly at the time of assembly and that there are not multiple faults present.

There is a continuous self-diagnosis on certain control functions. This diagnostic capability is complemented by the diagnostic procedures contained in this manual. The language of communicating the source of the malfunction is a system of diagnostic trouble codes. When a malfunction is detected by the control module, a diagnostic trouble code is set and the Malfunction Indicator Lamp (MIL) "Service Engine Soon" is illuminated on some applications.