- 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 PREPARATIONS
All of the Diagnostic procedures have specific conditions under which each test is to be performed. Basic conditions that apply to all tests are:

- Battery in good condition and fully charged.
- Adequate fuel in the fuel tank.
- Fuel is uncontaminated.
- Service components in good condition (Fuel Filter, Spark Plugs)

Read each test procedure carefully to determine additional test conditions.

DIAGNOSTIC INFORMATION
1. Following a "Flow of Diagnosis" will usually lead to the correct test procedure and help repair the problem.

2. The Diagnostic Circuit Check should ALWAYS be performed whether or not a computer related problem is suspected. The "Diagnostic Circuit Check" may reveal computer problems which were not originally suspected. Bypassing this test during diagnosis may lead to replacement of good parts.

3. If test procedures cannot fix the problem (or not available), you can find additional component and system information in these areas:

^ A-Charts (System Testing) - may contain useful system descriptions, circuit description, wiring diagrams or diagnostic notes. Look here to see if the system you are working on has a related system test. You may perform these tests even if you have not been directed (unless otherwise noted).

^ C-Charts (Component Testing) - may contain useful component descriptions, circuit description, wiring diagrams or diagnostic notes. Look here to see if the component you are working on has a specific component test. You may perform these tests even if you have not been directed (unless otherwise noted).

^ Diagnostic Trouble Code Charts - includes circuit descriptions and flow charts to pinpoint a driveability problem. Normally the on-board computer will store a numeric code at the time of the occurance which can be interpreted at a later time when the particular circuit at fault can be scruntinized.

^ Diagnosis by Symptoms - These testing procedures should be used when no computer related problems appear and there is a problem that can be verified by a particular symptom.

^ System or Component Descriptions - Sometimes getting a better idea of HOW the system or component works can help with diagnosis of a problem.

NOTES:
^ Trouble Code charts should NEVER be used to diagnose a component unless that trouble code has been stored. Using the trouble code chart without a stored trouble code may lead to incorrect diagnosis and replacement of good parts.

^ The charts or tests mentioned may not be available for the specific vehicle you are working on.

^ The charts or tests mentioned are located under Computers and Control Systems / Testing and Inspection / Procedures. Testing and Inspection