Engine and gearbox (P)
P0135: O2 sensor heater circuit fault
This code indicates a problem with the heater circuit of the upstream oxygen sensor. The heater helps the sensor reach operating temperature quickly for accurate readings.
Checked by a licensed car technician · last reviewed 29 September 2026
Symptoms
- Increased fuel consumption
- Rough idle
- Check engine light on
Common causes
- Heater element failure
- Power supply issue
- Wiring fault
How to check it yourself
- Inspect heater circuit voltage
- Check fuse and wiring integrity
- Test oxygen sensor heater element
Can I keep driving?
The car can still be driven, but fuel efficiency may be reduced.
General guidance, not a professional inspection. Confirm faults with measurements before buying parts, and use a qualified mechanic for brakes, steering, fuel leaks, airbags, and other safety-critical work. Terms and disclaimer