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.
1993 Lexus SC 300 AutomaticFACTORY OEM SERVICE PROCEDURE
Code 25
Condition is one of the following:
- Main oxygen sensor voltage is 0.5 volt or less 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.
- On GS300 and SC300, difference of air/fuel ratio feedback compensation value between front cylinders (No. 1-3) and rear cylinders (No. 4-6) is more than 15 percent for more than 20 seconds with engine speed more than 2000 RPM and engine temperature 140-203°F (60-95°C). Probable cause: open or short in fuel injector circuit, fuel pressure, stretched or defective timing belt, ignition system failure, low compression pressure, defective airflow meter or defective ECM.
- On ES300, difference of air/fuel ratio feedback compensation value between left and right banks is more than 15 percent for more than 20 seconds with engine idling and engine temperature 156-203°F (70-95°C). Probable cause: open or short in fuel injector circuit, fuel pressure, stretched or defective timing belt, ignition system failure, low compression pressure, defective airflow meter or defective ECM.
- On GS300 and SC300, engine speed varies by more than 15 RPM over the preceding crank angle period during a period of more than 20 seconds with engine idling and engine temperature 140-203°F (60-95°C). Probable cause: open or short in fuel injector circuit, fuel pressure, stretched or defective timing belt, ignition system failure, low compression pressure, defective airflow meter or defective ECM.
Factory Service Tools
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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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