P0135: O2 Sensor Heater Circuit (Bank 1 Sensor 1)
The heater built into the upstream oxygen sensor on bank 1 is not working, so the sensor takes too long to warm up.
What P0135 means
Oxygen sensors only work when they are hot, around 600 degrees F or more. To get there quickly after a cold start, each sensor has an electric heater inside. The engine computer powers that heater and watches the current it draws or how quickly the sensor starts working. P0135 sets when the bank 1 sensor 1 heater circuit is open, shorted or drawing the wrong current. Since the heater is part of the sensor, a burned out element is the most common cause and the fix is a new sensor. A blown fuse or damaged wiring can cause it too, and if several heater codes appear at once, a shared fuse is a good bet. KBB notes the code may cause poor fuel economy and carbon build up but short trips usually will not cause mechanical damage. Shops measure heater resistance and check for power and ground at the connector. It is a common and fairly simple repair.
Common symptoms
- Check engine light on
- Worse gas mileage right after starting
- Higher emissions
- Rough running on cold starts in some cars
- Often no other symptoms
Most common causes
- Burned out heater element inside the oxygen sensor
- Blown oxygen sensor heater fuse
- Open or shorted heater wiring
- Corroded connector
- Engine computer heater driver fault (rare)
What to check yourself first
Check the fuse that feeds the oxygen sensor heaters, often labeled O2 or HO2S in the fuse box. Unplug the sensor and measure heater resistance across the two heater pins with a meter; most read a few ohms, while an open reading means a dead heater.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace oxygen sensor | $440-$523 | The heater is built into the sensor, so a failed heater means a new sensor. |
| Electrical diagnosis to find a wiring or connector fault | $122-$179 | If the fuse or wiring feeding the heater is the problem. |
| Check engine light diagnosis at a shop | $125-$183 | Confirms power, ground and heater resistance before parts are bought. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0030 HO2S Heater Control Circuit (Bank 1 Sensor 1)
- P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2)
- P0155 O2 Sensor Heater Circuit (Bank 2 Sensor 1)
- P0134 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
- P0130 O2 Sensor Circuit (Bank 1 Sensor 1)