How to Use Diagnostic Routines

HOW TO USE THE DIAGNOSTIC PROCEDURES
- Use the information about the vehicle driveability or emission concern (from the service write-up or the Customer Information Worksheet) 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 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.
- 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 or a Pinpoint Test Step), go to the procedures. Follow the direction given, including directions to other tests or 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 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 symptom is eliminated.

NOTE: If a symptom is determined to be intermiffent, a careful visual and physical underhood inspection of connectors, wiring harnesses, vacuum lines, 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.