- Important Preliminary Checks

BEFORE STARTING
Before using Diagnosis by Symptom you should have performed the On-Board Diagnostic System Check and determined that: Testing and Inspection

1. The Powertrain Control Module (PCM) and Malfunction Indicator Lamp (MIL) (Service Engine Soon) are operating correctly.
2. There are no Diagnostic Trouble Codes (DTCs) stored.
3. Tech 1 scanner data is within normal operating range. Typical scan data values are listed in System Diagnosis/Procedures/Scan-Tool Diagnostics/Engine Scan Data Values. Engine Scan Data Values

SYMPTOM
Verify the customer complaint, and locate the correct symptom in this section. Check the items indicated under that symptom.

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

^ PCM 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.
^ Mass Air Flow (MAF) sensor installation. The arrows on the plastic portion of the sensor must point toward the engine.
^ Air Intake ducts for collapsed or damaged areas.
^ Air leaks at throttle body mounting area, MAF sensor and intake manifold sealing surfaces.
^ Ignition wires for cracking, hardness, proper routing and carbon tracking.
^ Wiring for proper connections, pinches and cuts.