- 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 2 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
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 vacuum hoses for the following conditions:

- Correct routing
- Pinches
- Cuts
- 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 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.

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 system. 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.