P0135: The upstream oxygen sensor heater on the driver side is not working
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
The heater in the upstream oxygen sensor has a fault (bank 1). Get it checked within a week or two. If the engine runs rough or the light flashes, stop driving.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
Your upstream oxygen sensor has a small built-in heater that brings it to operating temperature within about 30 seconds of start-up. When that heater circuit fails, the sensor takes much longer to warm up, so the engine runs on an open-loop fuel estimate for an extended time at every cold start. P0135 means the computer measured heater circuit current or resistance outside the expected range. The sensor itself may still work fine once warm. The problem is the heater element or the wiring that feeds it.
Common causes
- Failed O2 sensor heater elementThe heater inside the sensor burns out with age. Most common cause, especially on cars past 80,000 miles.
- Blown fuse for the O2 sensor heater circuitCheck the fuse box before replacing the sensor. A fuse can save you a sensor.
- Damaged or corroded wiring to the sensorHeat cycles under the hood crack insulation and corrode connectors over time.
- Failed powertrain control module output driverRare, but the PCM controls the heater ground circuit. A bad driver will read like a sensor failure.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- Fuse replacement
- Wiring repair or connector replacement
- Upstream O2 sensor (Bank 1)
Symptoms
- Check engine light on, steady
- Slightly worse fuel economy, especially on short trips
- Possibly rough or rich running for a minute or two after a cold start
- Failed emissions test
What to do next
Pull the fuse diagram and check the O2 sensor heater fuse first. If that is fine, inspect the sensor connector for corrosion or melted insulation near the exhaust manifold. If the wiring looks good, the sensor element itself has failed and needs replacement. Bank 1 is the side of the engine that contains cylinder 1, usually the driver side on most American and Japanese vehicles. Confirm which side before ordering a part.
Lewis shows the live upstream oxygen sensor voltage, so after a heater repair you can see whether the sensor starts responding quickly from a cold start. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Is P0135 the same as a bad oxygen sensor?
- Not always. The heater circuit is separate from the sensing element. The sensor may still read correctly once warm. Confirm the actual sensor output before replacing it.
- Can I pass emissions with P0135?
- No. Any stored oxygen sensor code is an automatic emissions failure in OBD2 testing states.
- Does Bank 1 Sensor 1 mean upstream or downstream?
- Sensor 1 is always upstream, before the catalytic converter. Sensor 2 is downstream, after it.
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