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 Circuit Check
The Diagnostic Circuit Check is a starting point in identifying a fuel injection system problem. The ECM will flash Code 12 through the CHECK ENGINE light. This indicates self-diagnostics are working.
Code 12 will not flash 3 times if other codes are stored in memory. Each additional code will flash 3 times. Codes start with the lowest number code. If no codes are present, Code 12 will flash until fuse is removed from fuse block.
Record all codes stored except Code 12. If problem is that engine cranks but will not run, see BASIC TESTING article. If no additional codes were recorded, refer to TESTS W/O CODES article.
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.