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 Procedure
Diagnosis of computerized 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. Perform ON-BOARD DIAGNOSTIC SYSTEM CHECK before diagnosing Diagnostic Trouble Codes (DTCs).
- If DTC(s) were displayed, determine whether codes are hard or intermittent trouble codes. Hard codes will cause MIL to illuminate continuously while engine is running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION . For diagnosing hard codes, proceed to appropriate DTC test. See DIAGNOSTIC TESTS . For diagnosing intermittent codes, proceed to INTERMITTENTS in appropriate TROUBLE SHOOTING - NO CODES article.
- If no DTCs are present and a driveability problem exists, refer to SYMPTOMS in appropriate TROUBLE SHOOTING - NO CODES article. Doing so will help identify proper system or component to check. See appropriate SYSTEM & COMPONENT TESTING article for diagnosis of faulty component.
- After necessary repairs are made, clear DTCs, verify vehicle will enter "closed-loop" operation, and ensure DTC does not reset.
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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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