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 monitors Heated Oxygen Sensor (HO2S) activity for 90 seconds. PCM determines if HO2S 1 is functioning properly by counting number of HO2S 1 Lean/Rich (L/R) and Rich/Lean(R/L) switches. If PCM determines that HO2S 1 did not switch enough times, DTC 1133 is set.
Conditions required to set DTC are:
- ECT above 122°F (50°C).
- Engine running at least one minute.
- Canister purge duty cycle is greater than two percent.
- Engine speed between 1500-3000 RPM.
- 90 seconds after closed loop, PCM monitors oxygen sensor as it switches above and below .45 volts. If less than 40 rich -to-lean and lean-to-rich switches are detected, DTC P1133 will be set.
- Engine operating in closed loop mode.
- Above conditions present for 3 seconds.
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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.