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 P0135, Heated Oxygen Sensor Heater Circuit Malfunction "S" & "T" Series 4.3L (VIN W) Bank 1, Sensor 1: Notes
Control module supplies and monitors voltage of about .45 volt between control module HO2S low reference circuit and HO2S signal circuit. If read with a 10 megohm DVOM, voltage may read as low as .32 volt. HO2S varies voltage within a range of about 1 volt (rich) to .10 volt (lean). Sensor is like an open circuit and produces no voltage when less than about 600°F (360°C).
- Determines if code is result of a hard failure or an intermittent condition.
- Verifies voltage is present at heater.
- If voltage is available at connector, it is a good voltage source to check for a good sensor ground.
- Determines if voltage is not available at sensor due to an open fuse or open in ignition feed 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.