MotorBitP0135: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
The upstream oxygen sensor heater on bank 1 failed. The light can come on shortly after startup.
Educational OBD2 information. Confirm on your vehicle with a scan tool. MotorBit can read this code, freeze frame, and live data over an ELM327 adapter.
What P0135 means
The PCM monitors heater current. Open, short, or high resistance sets P0135.
Why the check engine light comes on
Without a working heater, the sensor stays cold, fuel control is delayed, and emissions rise on cold start.
Common causes
- Failed O2 sensor heater
- Blown fuse
- Wiring damage
- PCM driver issue (rare)
Typical symptoms
- MIL
- Possible rich smell on cold start
- Often drives normally once warm
What to do next
- Check the heater fuse first.
- Inspect the sensor connector for water/corrosion.
- Replace bank 1 sensor 1 if the heater is open.
How MotorBit helps
Open MotorBit, connect your ELM327, and read P0135 with freeze frame (RPM, load, temperature, speed at the moment the fault set). Then watch live PIDs and fuel trims instead of replacing parts by guesswork. When the repair is verified, clear the code and re-check monitors.
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FAQ
Is P0135 serious?
Severity is listed as medium on this page. Misfire, crank/cam, and communication codes deserve faster attention than a tiny EVAP leak.
Will disconnecting the battery clear P0135?
It may hide the lamp temporarily, but the fault usually returns and you lose freeze-frame evidence. Scan first, then clear after the repair.
Can MotorBit clear P0135?
Yes, after you understand the cause. Clearing without a repair is how the light comes back on the next drive cycle.