Diagnostic Mode

The SES light will flash a Code 12, indicating the self-diagnostic system is operating. If SES light does not flash, see DIAGNOSTIC CIRCUIT CHECK in this article. A Code 12 consists of one flash followed by a short pause and then two quick flashes. This code will be repeated 3 times. If Code 12 continues to flash (more than 3 times), no codes are stored in ECM memory. Code 12 will continue to flash until diagnostic terminal to ground circuit is interrupted.

If codes are stored in memory they will be output after the initial Code 12. Each code will be repeated 3 times in the same manner. Record all codes for reference.

The ECM will energize all solenoids and relays (except fuel pump relay) during diagnostic mode. The Idle Air Control Valve (IACV) signal will be checked by the ECM and the valve moved to the fully extended position.