- Flow of Diagnosis - Start Here

When diagnosing system malfunctions, all procedures must be performed in proper sequence to ensure accurate results. Although there are several charts associated with system diagnosis, if proper procedure is followed, only a few charts are needed to prove that system is operating properly, and normally only 3 charts are needed to locate a malfunction. When diagnosing suspected system malfunctions, proceed as follows:

Diagnostic charts referred to under System Diagnosis are related to the ECM and will determine whether the Electronic Control Module (ECM) is operating properly. Following proper diagnostic sequence is essential to determining whether the ECM and related components are operating properly; whether the malfunction is current or intermittent; or whether the malfunction is related to the electronic control system.

1. Perform thorough underhood inspection. Ensure all components are properly mounted, wiring harnesses and vacuum hoses are properly routed, connectors are fully seated, and connector terminals are making proper contact.

2. Perform the ``Diagnostic Circuit Check,'' carefully following all steps. Testing and Inspection

3. Proceed with tests indicated by diagnostic circuit check, noting the following:

a. Perform all steps necessary to ensure self-diagnostic feature is operating properly.
b. If available, use SCAN tool to monitor ECM data.
c. If engine fails to start, refer to A-Charts to correct no start condition.

d. Review stored trouble codes, determine whether trouble codes are ``hard'' codes or whether malfunction is intermittent, and proceed with the applicable trouble code diagnosis.

e. If no codes are stored, Refer to Diagnosis by Symptom and test ECM related systems that do not set trouble codes as outlined.

f. If malfunction is intermittent, refer to Intermittents in Diagnosis by Symptom, perform SCAN tests under conditions necessary to produce malfunction, and repair systems as needed.