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 21 (Except GS300 Calif.)
Condition is: main oxygen sensor signal voltage is reduced to 0.4-0.7 volt for 90 seconds with the following conditions. Engine temperature 158-195°F (70-91°C), engine speed more than 1500 RPM and under a load. Probable cause: defective main oxygen sensor (front sensor on GS300 and SC300 or left bank sensor on ES300).
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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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