What P0135 Means
The heater built into the oxygen sensor (which helps it reach operating temperature quickly) has an electrical fault.
Common Causes
- Failed oxygen sensor heater element
- Damaged or corroded sensor wiring/connector
- Blown fuse for the O2 sensor heater circuit
Symptoms You Might Notice
- Usually no immediate drivability symptoms
- Check engine light on
- Slightly worse fuel economy and emissions until the sensor fully warms up during driving
What to Check First
- 1
Check the fuse for the O2 sensor heater circuit first — it's the cheapest thing to rule out
- 2
Inspect the sensor's wiring and connector for damage or corrosion
- 3
Test the heater circuit's resistance; replace the sensor if the heater element itself has failed