- Diagnostic Procedure

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

2. The On-Board Diagnostic (OBD) System Check (under Computers and Control Systems/ Testing and Inspection) should ALWAYS be performed whether or not a computer related problem is suspected. The "On-Board Diagnostic System Check" may reveal computer problems which were not originally suspected. Bypassing this test during diagnosis may lead to replacement of good parts.
Testing and Inspection

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

^ Diagnostic Charts - 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). See Computers and Control Systems/Testing and Inspection/Procedures/Diagnostic Charts.
Testing and Inspection


^ Diagnostic Trouble Code Charts - may be reviewed for diagnostic notes and circuit descriptions.
Testing and Inspection




CAUTION:
- 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.

^ Diagnosis by Symptom - should be used when no computer related problems appear. See Also Diagnosis by Symptoms under Fuel Systems, Ignition Systems and Emission Systems. Refer to Computers and Control Systems/System Diagnosis. Testing and Inspection

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