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
PCM provides about 0.45 volt reference to Heated Oxygen Sensor (HO2S). HO2S sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. PCM counts number or times a rich-to-lean and lean-to-rich response is indicated and adds amount of time it takes to complete all transitions. PCM uses this information to determine average time for each transition. If average response time is slow, DTC P0133 will set.
Conditions required to set DTC are:
- No CKP, ECT, EGR pintle position, IAT, MAF, MAP or TP sensor DTCs set.
- No EVAP system DTC set.
- No fuel injector circuit, fuel trim or misfire DTCs set.
- Engine running in closed loop fuel mode for at least one minute.
- Engine speed 1000-3000 RPM.
- ECT greater than 185°F (85°C).
- MAF 15-28 grams per second.
- Lean-to-rich average transition response time greater than 153 milliseconds.
- Rich-to-lean average transition response time greater than 148 milliseconds.
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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.