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.
Code 25
Condition is one of the following:
* Main oxygen sensor voltage is 0.5 volt or less (lean) for 90 seconds with engine speed more than 1500 RPM and coolant temperature more than 158°F (70°C). Probable cause: open or short in main oxygen sensor circuit, defective main oxygen sensor, ignition circuit fault or defective ECM.
* Difference of air/fuel ratio feedback compensation value between left and right banks is more than 10 percent for more than 30 seconds with engine speed more than 2000 RPM and engine temperature 140-203°F (60-95°C). Probable cause: fuel pressure, stretched or defective timing belt or ignition system failure.
* Main oxygen sensor voltage is alternating above and below 0.5 volt at 5 times per second or more with engine idling and engine temperature 140-203°F (60-95°C). Probable cause: open or short in injector circuit, fuel pressure, defective airflow meter, engine ground bolt loose or foreign object caught in valve.
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.