P0135: O2 Sensor Heater Circuit, Bank 1 Sensor 1
P0135 means the control module found a problem with the heater circuit of the upstream oxygen sensor on bank 1. The car usually keeps running, but it burns more fuel and produces more emissions after a cold start until the problem is fixed.
You can drive, but get it checked soon
The data lists no limp mode for this code, so the car normally drives. Until it is repaired, it runs without mixture control for longer after a cold start, which uses more fuel and raises emissions, so get it fixed soon.
What it means
The upstream oxygen sensor (bank 1, sensor 1) measures the oxygen in the exhaust so the engine computer can adjust the fuel mixture. It has a built-in electric heater so it reaches its working temperature of about 300 °C soon after a cold start. The control module switches the heater on and checks the heater's voltage and current. If the current falls outside the range the manufacturer allows, it sets P0135 and turns on the check engine light. Manufacturers split heater faults differently between P0030–P0032, P0053 and P0135, so the exact trigger depends on the vehicle. With a dead heater, closed-loop control (the mode where the computer fine-tunes the mixture using sensor feedback) starts late after a cold start.
Likely causes
- Heater element of the sensor burnt outVery likely
The heater inside the sensor is the most common failure point, and a burnt-out heater means the sensor must be replaced.
- Fuse or relay of the heater supply faultyPossible
If the heater gets no power, the module sees no heater current and sets the code.
- Heater wiring or connector open, corroded or shortedPossible
A break, corrosion or short in the circuit stops the correct current from flowing through the heater.
- Unsuitable replacement sensorLess likely
A sensor with a different heater resistance can draw current outside the range the module expects.
- Heater driver in the control module faultyLess likely
The module switches the heater on the ground side, and a failed driver cannot do that correctly.
What you may notice
- Check engine light on
- Longer cold-start phase without mixture control, with more fuel use and emissions
- Follow-up codes P0133 or P0134 possible because the sensor stays cold
What to check, cheapest first
- 1Read all stored codes. If P0141 appears together with P0135, check the fuse they share first. · you can do it
- 2Check the fuse and relay for the oxygen sensor heater supply and replace any that are faulty. · you can do it
- 3Inspect the sensor's wiring and connector for damage, corrosion, loose pins or burnt insulation. · you can do it
- 4Measure the heater element's resistance and compare it with the specification for the vehicle. · mechanic
- 5Check the heater circuit for power, ground and the control signal from the module, including any open or short in the wiring. · mechanic
- 6If the heater is burnt out, replace the sensor with the correct type, clear the code and run a drive cycle to confirm the fix. Suspect the module's heater driver only after everything else checks out. · mechanic
Related codes
Frequently asked questions
Can I drive with P0135?+
Usually yes, since limp mode is not expected. The engine will use more fuel and emit more after a cold start, so repair it soon.
Can a loose gas cap cause P0135?+
No. P0135 is about the electrical heater circuit of the oxygen sensor, not the fuel system's vapor seal. The common causes are the sensor heater, fuse, relay or wiring.
Will P0135 pass an emissions test?+
Probably not. The check engine light is on and the code is emissions-relevant. After the repair, a drive cycle is required before the monitors are ready again.
Can I fix it myself?+
Often yes. The repair is rated easy and DIY is possible, at roughly 0.2 to 1.5 hours depending on whether it is a fuse, wiring or the sensor.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10