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 Aids
Fuel-contaminated engine oil may affect some codes. If oil is suspect, remove PCV valve from valve cover and repeat QUICK TEST . If problem is corrected, change engine oil.
On CIRCUIT TEST H and CIRCUIT TEST J, vacuum leaks in non-EEC related areas may cause Code 41 or 91 to be displayed. Check vacuum motors, engine seals, EGR system, PCV system, Canister Purge (CANP), HEGO sensor and between airflow meter and throttle body for unmetered air leaks. Code 42 or 92 may be caused by fuel-contaminated engine oil, ignition misfire, or EGR system or CANP problems.
CIRCUIT TESTS are grouped as follows:
- A-C - No Start & Voltage Tests.
- DA-DS - Input Sensor Tests.
- FD-FF - Additional Input Component Tests.
- G-J - Fuel Control Systems.
- KC-X - ECA (Processor) Output Tests.
NO RELATED
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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.