- Diagnostic Procedure

^ Before using this section you should have performed the DFI SYSTEM CHECK and the SELF-DIAGNOSTIC CIRCUIT CHECK which verifies the "SERVICE ENGINE SOON" and "SERVICE VEHICLE SOON" lamps are operational, the fuel system is functioning properly, as well as no trouble codes were retrieved.
^ Always use the FLOW OF DIAGNOSIS for proper testing sequence.
^ If the ENGINE CRANKS BUT WILL NOT RUN, use CHART A-3 in DIAGNOSTIC CHARTS/A-CHARTS.
^ 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 driveablity 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:
^ ECM/BCM 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. These procedures are not
meant to be done in consecutive order. If "Parameter" readings do not indicate
a problem, then proceed in a logical order, easiest to check or most the
likely cause first. To determine if a particular system or component is
used on a specific vehicle, refer to the ECM/BCM Wiring Diagrams in
ELECTRICAL AND ELECTRONIC DIAGRAMS for application.