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.
Testing Procedure
Diagnosis of engine control system should be performed in the following order:
- Ensure all engine systems not related to computer are operating properly. Check for any Technical Service Bulletins (TSBs) that may apply. DO NOT proceed with testing unless all other problems have been repaired.
- Start engine and check MIL. If MIL stays on, enter diagnostics and determine if DTCs are present. See RETRIEVING DIAGNOSTIC TROUBLE CODES . If DTCs were displayed, determine whether codes are hard or intermittent trouble codes. Hard codes will cause MIL to illuminate continuously while engine is running. See ON-BOARD DIAGNOSTICS under SELF-DIAGNOSTIC SYSTEM. For diagnosing hard codes, proceed to appropriate DTC test. See DIAGNOSTIC TROUBLE CODE IDENTIFICATION . For diagnosing intermittent codes, proceed to INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
- If MIL stays on, and no DTCs are present, or if MIL does not come on, check MIL. See MALFUNCTION INDICATOR LIGHT CIRCUIT DIAGNOSIS .
- If no DTCs are present and a driveability problem exists, refer to INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. Doing so will help identify proper system or component to check. See SYSTEM & COMPONENT TESTING article for diagnosis of faulty component.
- After necessary repairs are made, perform final procedure. See FINAL PROCEDURE .
Use the Manual With the Right Hardware
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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.
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