P0155: O2 Sensor Heater Circuit (Bank 2 Sensor 1)
P0155 means O2 Sensor Heater Circuit (Bank 2 Sensor 1). Oxygen sensors only produce a useful signal when they are hot, so they contain an electric heater. This code points to a problem in the heater circuit of the oxygen sensor on bank 2 (the side opposite cylinder 1), sensor 1 (upstream, before the catalytic converter). The control module has detected a fault in the circuit itself, such as an open circuit, a short, or a signal outside the electrical limits it expects.
Can I keep driving? Safe to drive short-term, but have it checked to avoid failed emissions or worse fuel economy.
Common symptoms
- Check engine light on
- Usually no noticeable drivability change
- Engine may take longer to enter closed-loop fuel control after a cold start
- Can cause a failed emissions inspection
Possible causes
- Burned-out heater element inside the oxygen sensor
- Blown fuse for the heater circuit
- Damaged wiring or connector (often near the exhaust)
- Engine computer heater driver fault (rare)
How to diagnose P0155
- Check the fuse that supplies the oxygen sensor heaters.
- Unplug the sensor and measure heater resistance; compare with the service specification.
- Check for battery voltage on the heater supply wire with the engine running.
- Inspect the harness for melted or chafed sections near the exhaust.
What the code means, digit by digit
Generic codes have the same definition on every OBD-II vehicle (petrol cars from model year 1996 in the US, 2001 in the EU; diesels later). Manufacturers can add their own enhanced codes; those are not listed here.
Related codes
- P0161 O2 Sensor Heater Circuit (Bank 2 Sensor 2)
- P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2)
- P0135 O2 Sensor Heater Circuit (Bank 1 Sensor 1)
- P0058 HO2S Heater Control Circuit High (Bank 2 Sensor 2)
- P0057 HO2S Heater Control Circuit Low (Bank 2 Sensor 2)
- P0056 HO2S Heater Control Circuit (Bank 2 Sensor 2)
- P0052 HO2S Heater Control Circuit High (Bank 2 Sensor 1)
- P0051 HO2S Heater Control Circuit Low (Bank 2 Sensor 1)
General guidance only. Fault codes describe what the engine computer saw, not which part failed: confirm with testing before replacing parts, and follow the vehicle's service information.