Diagnostic Modes

Fig. 52 - ECM Terminal Identification:

Fig. 53 - Connector Terminal Arrangement:

A built-in, self diagnostic system will identify problems most likely to occur in the Throttle Body Fuel Injection System. When a problem is detected, the diagnostic system will illuminate a "Check Engine" or "Service Engine Soon" light in the instrument panel. The "Check Engine" light will flash a trouble code or codes when a trouble code "Test" terminal under the dash is grounded with ignition on and engine not running.
The "Check Engine" or "Service Engine Soon" light will illuminate with the ignition switch on and the engine not running. If the "Test" terminal is then grounded and the light flashes a Code 12, the self-diagnostic system is functioning properly. A Code 12 consists of one flash, a short pause, then two flashes in rapid succession. After a longer pause, the code will repeat two more times.
When the engine is started, the "Check Engine" or "Service Engine Soon" light should turn off. If the light remains lit, the self-diagnostic system has detected a problem. To determine where the problem exists, ground the "Test" terminal with ignition on and engine not running and observe trouble code display. Each trouble code will flash three times in numeric order. Each trouble code will indicate a fault in a particular circuit. To diagnose the problem, refer to procedure given for appropriate trouble code.