Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.