P0135: O2 Sensor Heater Circuit (Bank 1 Sensor 1)
The heater circuit of the front oxygen sensor on bank 1 has a fault.
Normal risk
Safe to drive. Emissions are higher after a cold start. Fix it soon.
Short answer · Can I keep driving with P0135?
Yes. The sensor takes longer to work after a cold start, which raises emissions and fuel use slightly. Check the fuse first, then the sensor heater.
What does P0135 mean?
Oxygen sensors need to be very hot to work. A heater inside the sensor brings it up to temperature quickly. Code P0135 means the engine control unit detected a fault in the heater circuit of the front sensor on bank 1: often a failed heater element, a blown fuse or damaged wiring.
What the car does when the code is set
The check engine light comes on. The car drives normally. After a cold start the engine relies on default values for longer before it uses the sensor, so emissions are higher for the first minutes. Some emission readiness tests will not complete.
How the system works
Oxygen sensors only produce a useful signal when their tip is several hundred degrees hot. Exhaust heat alone takes minutes to get there, so each sensor has an electric heater. The engine control unit switches the heater on and off and monitors its current or resistance. If the current is too low (open circuit), too high (short) or the sensor does not warm up in time, it stores a heater code for that sensor. While the heater does not work, the engine relies on default values for longer after a cold start.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Failed heater elementThe heater inside the sensor burns out.
- Blown fuseMany cars have a separate fuse for the sensor heaters.
- Wiring or connector damageThe wiring runs near the hot exhaust and can melt or chafe.
- Control unit driver faultRare: the control unit no longer switches the heater.
How it is diagnosed
- Check the fuseFind the oxygen sensor heater fuse in the owner's manual or fuse box lid.
- Inspect the wiringFollow the wiring from the sensor and look for heat damage or chafing.
- Measure heater resistanceUnplug the sensor and measure the resistance of the heater pins. Compare with the service data; an open circuit means the sensor needs replacing.
- Check the supplyWith the ignition on, check the heater supply voltage at the connector.The exhaust and sensors are very hot after driving.
Questions about P0135
Why does the sensor need a heater?
Oxygen sensors work only when hot. The heater brings them to temperature quickly after a cold start, so the engine can use them sooner.
Can I drive long distances with a heater code?
Yes, it does not harm the engine. Emissions after cold starts are higher and some emission monitors will not complete.