What does P0155 mean?
The control module detected a condition described as “Oxygen-sensor heater bank 2 sensor 1 – fault”. The code identifies the affected area, but it does not by itself prove which component has failed. The code describes the detected condition, not a guaranteed failed part. A reliable diagnosis also considers related codes, freeze-frame data, live values and the actual symptoms.
Possible causes
- Aged or contaminated oxygen sensor
- Exhaust leak before or near the sensor
- Heater circuit, fuse, wiring or connector fault
- Air leak, fuel-pressure or injection problem affecting the mixture
Common symptoms
- Check-engine light
- Increased fuel consumption
- Rough running or poor throttle response
- Abnormal exhaust readings
Sensible next checks
- Monitor oxygen-sensor or wideband values in live data
- Compare short- and long-term fuel trims
- Inspect the exhaust system for leaks
- Test the heater circuit electrically using the correct wiring diagram
Why does it return after clearing?
Clearing the code only removes the stored entry. If the underlying condition remains, the control module will set the code again after the next relevant monitor cycle. Save the data first, diagnose the cause, repair it and only then clear the code.