Diagnostic Notes

^ Always use the FLOW OF DIAGNOSIS for proper testing sequence.
^ Several of the following symptom procedures call for a careful visual/physical check. This step is very important - it can lead to correcting a problem without further checks and can save valuable time.


NOTE: It is essential that the vehicle has been properly warmed up and is at operating temperature, except when attempting to diagnose a cold driveability problem. The catalytic converter and feedback system will not function as designed if this is not achieved. Failure to do so will result in inaccurate test results. Verify the correct symptom from the customer.

CHECK THE FOLLOWING:

^ MCU grounds for being clean, tight, and in their proper location.
^ Vacuum hoses for 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.
^ The following symptom charts contain groups of possible causes for each symptom and cover several engines. To determine if a particular system or component is used on a specific vehicle, refer to Powertrain Management/Computers and Control Systems/Diagrams/Electrical for application.