- Flow of Diagnosis - Start Here

1. Do the on-car diagnostics work? - Perform the Diagnostic Circuit Check.
- If the on-car diagnostics aren't working, this check will direct you to A-CHARTS DIAGNOSIS BY SYMPTOMS to repair the on-car diagnostics.
- If the car will not start, go to A-CHARTS DIAGNOSIS BY SYMPTOM, Chart A-3 Engine Cranks But Will Not Run.
2. If the on-car diagnostics are OK check to see if a trouble code is stored. If a trouble code is stored go to the trouble code number in TROUBLE CODE TEST CHARTS.
3. Is the fuel control system functioning properly? according to the Diagnostic Circuit Check and the Field Service Mode Check.
- If the fuel system is not controlling correctly, go to A-CHARTS DIAGNOSIS BY SYMPTOM. If the Field Service Mode Check shows that the system is in closed loop and working properly, go to DIAGNOSIS BY SYMPTOM. DIAGNOSIS BY SYMPTOM lists several driveablity symptoms and suggests checks of related components, which may be found in C-CHARTS COMPONENT TESTING.

VISUAL CHECK
A careful under the hood visual check often leads to repairing the vehicle without further steps.
- Inspect all vacuum hoses for pinches, cuts, or disconnects.
- Be sure to inspect hoses that may not easily be seen, hidden by the alternator, A/C compressor air cleaner etc. Inspect all electrical wires in the same way, for tight connections, burning, chaffing, or pinches.

A THOROUGH VISUAL CHECK CAN SAVE DIAGNOSTIC TIME.

CAUTION: When connecting power to the ECM--after replacement--the ignition switch must be OFF to prevent internal ECM damage.

1. If diagnostic procedures call for replacement of the ECM, verify that the current PROM is correct.

2. If it is correct, remove the PROM from the defective ECM and install it in the new ECM--as the new ECM will not contain a PROM.

NOTE: Prior to replacing any component as called for in the diagnostic procedures check the following:

1. Disconnect associated connector(s) and check for improper installation, bent, broken, or dirty terminals or mating tabs--repair or replace as required.
2. Connect all connectors and check the system to ensure that the problem has been corrected.

CAUTION: Any repairs made to wiring harness should be made with the battery disconnected to prevent damaging the harness.

NOTE: Disconnecting battery will erase all trouble codes stored in the ECM.