Diagnostic Notes

1) Verify Problem

Note: For catalytic converter and feedback system to function properly, it is essential that vehicle is at operating temperature, (except when attempting to diagnose cold start or cold driveability problem).

2) Extract And Clear Fault Codes

Diagnose and repair any fault code related problems before proceeding with further diagnosis.

Note: Extracting fault codes verifies PCM and control system are operational.

3) Perform Visual Inspection:

- PCM grounds: clean, tight, and in their proper location.
- Vacuum hoses: splits, kinks and proper connections. 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, harness, proper routing, arcing and carbon tracking.
- Wiring for proper connections, pinches, and cuts.
- Harnesses (EST, ESC, etc...) for proper routing.

4) Check and Record Idle RPM

Warning: Be sure to apply parking brake and/or block wheels before performing any test with the engine running.

If vehicle is equipped with an automatic transaxle, test and record idle rpm when the vehicle is first brought into shop, to assist in diagnosing;

- Engine Stalling
- Creeping
- Hard Shifting

SEE Computers and Control Systems/ Testing And Inspection/ Procedures/ Component Tests/ Throttle Body Minimum Airflow Test procedure.


5) Proceed To Diagnosis By Symptom

Note: These charts contain possible causes of symptoms. Proceed in logical order, easiest to check or most likely cause first.