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
VCM supplies a voltage of about .45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to .1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.
HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S or HO2S circuit is open.
DTC will test when the following conditions are present:
- No ECT, EVAP, IAT, MAF, MAP or TP sensor DTCs are set.
- No intrusive test is in progress.
- No device controls are active.
- System voltage is at least 9 volts.
- Engine run time is greater than 2 minutes.
- HO2S voltage is between 351-551 mV.
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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.