Diagnostic Mode

The SERVICE ENGINE SOON light will flash a Code 12, indicating self-diagnostic system operation. If SERVICE ENGINE SOON 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. Code 12 will repeat 3 times. If Code 12 continues to flash (more than 3 times), no codes are stored in Electronic Control Module (ECM) memory.

Code 12 will continue to flash until diagnostic terminal to ground circuit is interrupted. Any additional codes stored in memory will follow Code 12. Each additional code is repeated 3 times. 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.