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.
Circuit Description
The rear Heated Oxygen Sensors (HO2S) are used to determine oxygen storage capability of the converter. The rear HO2S diagnostics will run after the sensor has been active for more than 80 seconds and catalyst temperature is greater than 1112°F (600°C). If ECM does not see the sensor output switching to greater than or less than a threshold for a certain time, ECM will command rich or lean status to make it switch. If sensor does not react within 100 seconds, DTC will set and sensor will default to open loop.
DTC will also set when:
- HO2S heater has been running for more than 3 minutes.
- Rear HO2S closed loop is active.
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.
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