- 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. 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:

- VCM and engine grounds are clean and tight.
- Battery B+ cables are clean and tight at the battery and all junction points.
- 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
The System Diagnostic Tables under Computers and Control Systems / System Diagnosis are designed to locate a faulty circuit or component through logic based on the process of elimination. The charts are prepared with the requirement that the vehicle functioned correctly at the time of assembly and that there are no multiple failures. Testing and Inspection

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