Engine Runs/Will Not Perform Self-Diagnostics

ENGINE RUNS/WILL NOT PERFORM DIAGNOSTIC TESTS

The way in which the engine runs can be a clue to the cause of a test problem. If the engine seems to run normally but will not complete a test or display computer data, the cause may be a wiring problem to the diagnostic connector that does not affect the rest of the system. If the engine runs poorly, the cause may be a poor control system ground or a computer voltage problem that affects the logic module or the entire system.

Refer to, "Testing The Diagnostic Connector", for instructions on checking the connector and its circuits.