- Important Preliminary Checks

BEFORE STARTING DIAGNOSIS BY SYMPTOM
Before using this section you should have performed the On-Board Diagnostic System Check and determined that:

1. The Engine Control Module (ECM) and the Malfunction Indicator Lamp (MIL) are operating normally.
2. That there are NO Diagnostic Trouble Codes (DTCs) stored, or that there is a DTC stored, but NO MIL.
Testing and Inspection

SYMPTOM
Verify the customer complaint, and locate the correct symptom under Diagnosis By Symptom. Check the items indicated under that symptom.

VISUAL AND PHYSICAL CHECKS
Several of the procedures under Diagnosis By Symptom call for careful visual and physical checks. The importance of this step cannot be stressed too strongly - it can lead to correcting a malfunction without further checks and can save valuable time. This check should include:

^ ECM grounds for being clean, tight, and in their proper location.
^ Vacuum hoses for splits, kinks and proper connections, as shown on the underhood Vehicle Emission Control Information Label. Check thoroughly for any type of leak or restriction.
^ Air leaks at throttle body mounting area and intake manifold sealing surfaces.
^ Ignition wires for cracking, hardness, proper routing and carbon tracking.
^ Wiring for proper connections, pinches, and cuts.