- Description of On-Board Diagnostics

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

2. The Diagnostic Circuit Check (under Computers and Control Systems/System Diagnosis) 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. 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:

^ 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. Refer to Computers And Control Systems/System Diagnosis/Diagnostic Charts/A Charts. Related Tests, Information and Procedures

^ C Charts (Component Testing) - Contains system and component diagnostic information including diagnostic flow charts, component descriptions, circuit description, wiring diagrams &/or diagnostic notes. Look here for system/component test procedures or functional checks. Refer to Computers And Control Systems/System Diagnosis/Diagnostic Charts/C Charts. Testing and Inspection

^ Diagnostic Trouble Code Charts - Use these charts for diagnosing trouble codes. May be reviewed for diagnostic notes and circuit descriptions. Refer to Computers And Control Systems/System Diagnosis/Diagnostic Charts/Diagnostic Trouble Code Charts. 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 Symptoms - Should be used to assist in diagnosing driveability problems when no trouble codes are present and no other computer related problems are apparent. 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.