How to Use the Diagnostic Procedures

How To Use The Diagnostic Procedures

- Use the information about the vehicle driveability or emission concern (from the service write-up, Customer Information Worksheet, etc.) to attempt to verify/re-create the symptom. Look for any vehicle modifications or aftermarket items that may contribute to the symptom. A check of any applicable TSBs or OASIS messages may be useful, if this information is available.
- Refer to the Symptom Index (Section 3) and select the symptom that best describes the vehicle symptom. (For multiple symptoms, select the one that is most noticeable.)
- Go to the Symptom Chart indicated in the Symptom Index.
- Begin the Chart at step number "1."
- Follow the instructions in the step (including Preliminary Checks, etc.)
- If the step contains a test procedure or question (without a reference outside the step), perform the test step/answer the question and continue as directed.
- If the step sends you to a specific area for testing (for example Hard Start/No Start Procedures, a Pinpoint Test Step in this manual or a Workshop Manual group), go to the procedures. Follow the directions given in those procedures, including directions to other tests, sections. If a damaged part is found, repair/replace as directed. If no fault is found, and diagnosis in that area is complete, return to the Symptom Chart and continue as directed.
- During diagnosis, if directed to test a system/component that is not contained on that vehicle, proceed to the next step.
- If the Symptom Chart for the vehicle symptom is completed and no fault is found, return to the Symptom Index to address the next most prominent symptom.
- After service, verify that the vehicle is operating properly and the original complaint is eliminated.

Note: If a symptom is determined to be intermittent, careful visual and physical underhood inspection of connectors, wiring harnesses, vacuum lines, and components is required. The Customer Information Worksheet may contain more detailed symptom information. Before an in-depth diagnosis begins, start the engine and wiggle wires, tap on components, etc., while listening for an indication of a concern (such as rpm change or relay clicking).

Information about engine conditions is stored when a Diagnostic Trouble Code (DTC) that lights the Malfunction Indicator Lamp (MIL) is set.