P0155 – O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
What does P0155 mean?
The heater circuit in the Bank 2 upstream oxygen sensor (Bank 2, Sensor 1) is malfunctioning. This is the Bank 2 counterpart to P0135 and only appears on engines with two cylinder banks.
What causes P0155?
Listed from most to least common:
- 1Failed oxygen sensor heater element
- 2Blown fuse in the heater circuit
- 3Damaged wiring or connector from exhaust heat
- 4Corroded connector
- 5Relay fault
Code breakdown
Common symptoms
- Check engine light on
- Slightly reduced fuel economy
- Usually normal drivability
- Failed emissions test
How to diagnose
- 1Check the heater circuit fuse first.
- 2Confirm which side of the engine is Bank 2 for your specific vehicle.
- 3Inspect the connector and harness for heat damage.
- 4Measure heater element resistance against specification.
- 5Verify battery voltage reaches the heater circuit with the key on.
The engine stays in open loop longer after cold start on that bank, hurting fuel economy and emissions.
Common fixes and estimated costs
| Repair | Estimated cost |
|---|---|
| Replace fuse | $5–$20 |
| Repair wiring/connector | $80–$300 |
| Replace Bank 2 upstream oxygen sensor | $150–$400 |
Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.
Good to know
If P0135 and P0155 appear together, suspect a shared fuse or relay rather than two sensors failing at once — that shared circuit is much more likely.
Related codes
This information is provided for general reference only and may vary by manufacturer, model, and year. It is not a substitute for professional diagnosis or repair.