OBD-II · P0135
P0135 Code: Upstream O2 Sensor Heater — Testing & Cost
O2 sensor heater circuit malfunction (Bank 1, Sensor 1)
The short version
Drivable, but the engine stays in open loop longer after a cold start, raising fuel use and failing emissions tests.
- Severity: Moderate
- Most common cause: Blown heater-circuit fuse or relay
- 5 diagnosis steps in order
- 4 symptoms tied to this code
Darker bars are the more common causes; bar length is the top expected repair cost. Start with the dark, cheap causes before the expensive ones.
Can I keep driving?
Drivable, but the engine stays in open loop longer after a cold start, raising fuel use and failing emissions tests.
Symptoms
- Check engine light with little drivability change
- Higher fuel consumption on short trips
- Emissions readiness monitors not completing
- Sensor readings slow to respond after a cold start
Causes & repair cost
Blown heater-circuit fuse or relay
Most common$5 – $60
Open heater element inside the sensor
Most common$120 – $380
Corroded connector or exhaust-heat damaged wiring
Possible$60 – $250
Poor ground in the heater circuit
Rare$60 – $200
ECM driver failure (rare)
Rare$400 – $1,200
A fuse is a few dollars; an upstream oxygen sensor runs $120–$380 installed. Labor rises if the sensor is seized in the manifold.
Estimate the repair for your carDiagnosis steps in order
- Check the fuse first; if it blows again there is a short in the wiring or sensor
- Measure heater resistance (typically 2–15 ohms depending on model)
- Confirm 12 V reaches the connector with the engine running
- Test the ground with a voltage-drop reading, not just continuity
- Use the correct anti-seize on the new sensor's threads
FAQ
Can I use a universal sensor?
It works but needs careful splicing; a direct-fit sensor with the factory connector is far less likely to re-set the code.
What is the difference from P0141?
P0135 is the upstream sensor before the converter; P0141 is the downstream one after it. Same testing, different location.
Will this code fail an emissions test?
Yes; the code leaves a readiness monitor incomplete, so the station rejects the car even after clearing.
Can a bad heater drain the battery?
Usually not; the circuit runs only with the engine on, and a short blows the fuse before draining the battery.
Related codes
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