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 P0134, Heated Oxygen Sensor Open Circuit: Notes
The PCM supplies and monitors voltage of approximately .45 volt between PCM HO2S low reference circuit (Tan wire) and HO2S signal circuit (Purple wire). If read with a 10 megohm DVOM, voltage may read as low as .32 volt. HO2S varies voltage within a range of approximately 1 volt (rich) to .10 volt (lean). Sensor is like an open circuit and produces no voltage when less than approximately 600°F (360°C). Open loop operation is caused by open oxygen sensor circuit or a cold sensor. Code P0134 will set when following conditions are present.
- Engine coolant temperature is greater than 110°F (43°C).
- Engine run time is more than 40 seconds.
- HO2S signal voltage is steady between .35-.56 volt.
- Throttle angle is greater than 3 percent.
- All conditions are met for approximately 30 or more seconds.
Code P0134 will cause system to operate in open loop. PCM will illuminate Malfunction Indicator Light (MIL).
- If conditions necessary to set Code P0132 exist, system will not go into closed loop.
- This will determine if sensor or wiring is cause of Code P0134.
- This test checks continuity in reference circuit.
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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.