P0135
O2 Sensor Heater Circuit Bank 1 Sensor 1
Emissions / O2 sensor
Generic OBD-II
Medium
What it means
P0135 means the ECM detected a fault in the heater circuit of the upstream oxygen sensor on bank 1 (the sensor before the catalytic converter). That heater brings the sensor up to operating temperature quickly so the engine can enter closed-loop fuel control sooner. The car drives normally, but until it's fixed the engine runs in open loop longer, hurting fuel economy and emissions.
Medium
Can I keep driving? Safe to drive — the car runs normally, but it stays in open loop longer, hurting economy and emissions until the sensor's heater is fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Slightly worse fuel economy (delayed entry into closed-loop fuel control)
- Failed emissions/readiness test
Common causes
Most likely first
- Failed heater element inside the upstream (bank 1, sensor 1) O2 sensor — most commonLikely
- Damaged wiring or a corroded connector at the sensorCommon
- Blown fuse or failed relay feeding the heater circuitCommon
- Open or short in the heater ground/control side, or rarely the ECMLess often
How to diagnose & fix
Work through it in order
- Check the fuse and relay that supply the O2-sensor heater first — the cheapest possible cause.
- Measure the heater element's resistance across its two heater pins and compare to spec; an open reading means a bad sensor.
- Inspect the connector and wiring for corrosion, melting, or breaks near the exhaust.
- Replace the upstream O2 sensor if the heater is open, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0135?+
Yes. The engine still runs and drives normally; the heater fault just slows how fast the sensor reaches operating temperature, so fuel trim and economy suffer slightly. It won't leave you stranded.
Can I just clear P0135?+
It will return once the ECM re-tests the heater, usually within a drive cycle or two. The fix is repairing the circuit or replacing the sensor, not clearing the code.
Related codes
Often seen with P0135
Read & clear P0135 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX