OBD-II code guide
P0135 Oxygen Sensor Heater Circuit Bank 1 Sensor 1
P0135 means the upstream oxygen sensor heater circuit is not working as expected.
What it means
The oxygen sensor may take too long to reach operating temperature, affecting fuel control and emissions.
Common symptoms
- Check engine light
- Poor cold-start fuel economy
- Failed emissions test
- Usually little drivability change
Likely causes
- Failed oxygen sensor heater
- Blown fuse
- Damaged wiring
- Poor connector contact
- PCM driver issue in rare cases
First checks
- Inspect wiring near the exhaust for heat damage.
- Check related fuses.
- Confirm bank and sensor location before replacing.
- Do not confuse sensor 1 with sensor 2.