P0155: Oxygen sensor heater (bank 2, sensor 1): circuit fault
The heater in the bank 2 oxygen sensor before the catalytic converter has a fault. Usually a blown fuse, the connector or the sensor itself.
| Code | P0155 |
|---|---|
| System | Engine and transmission |
| Group | P01xx, Air and fuel metering |
| Type | Generic: it means the same on every make |
| Can you keep driving? | Yes, no rush |
What P0155 means
The oxygen sensor before the catalytic converter measures how much oxygen is left in the exhaust, and the ECU uses that to fine-tune the air and fuel mixture. The sensor only works when it is very hot, so it has a small built-in heater that warms it up after a cold start. This code means the heater circuit has a fault. Bank 2 is the side of the engine opposite cylinder 1, and it only exists on V-shaped or boxer engines.
Most common causes
- Blown fuse for the oxygen sensor heaters
- Sensor connector loose or corroded
- Broken supply or earth wire to the heater
- Burnt-out heater element inside the sensor (the most common cause; the sensor has to be replaced)
- Faulty relay or ECU supply to the heater
Symptoms
- Engine warning light on
- Slightly higher consumption on short, cold journeys
- High emissions while the engine is cold
Can you drive with P0155?
Yes, no rush You can drive normally. When cold the mixture is controlled less precisely and the car uses a little more fuel, so do not leave the repair too long.
Open the bonnetthe in-depth explanation
How to check it
Look in the handbook for the fuse that feeds the oxygen sensor heaters and check it. If it is fine, a garage can measure the heater resistance at the sensor connector: with no continuity, the sensor needs replacing.
How to read and clear P0155 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0155 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P0151 Oxygen sensor (bank 2, sensor 1): voltage too low
- P0152 The lambda sensor (bank 2, sensor 1) gives a higher signal than normal
- P0153 Oxygen sensor (bank 2, sensor 1): slow response
- P0154 Heated lambda sensor 1 on bank 2 shows no activity
- P0156 Oxygen sensor (bank 2, sensor 2): circuit fault
- P0157 Oxygen sensor (bank 2, sensor 2): voltage too low
- P0158 Oxygen sensor (bank 2, sensor 2): voltage too high
- P0159 The lambda sensor circuit (bank 2, sensor 2) responds slowly
- P0100 Mass or volume air flow sensor circuit fault
- P0101 Air flow sensor range or performance problem
- P0102 Air flow sensor circuit low input
- P0103 Air flow sensor circuit high input
What does code P0155 mean?
The oxygen sensor before the catalytic converter measures how much oxygen is left in the exhaust, and the ECU uses that to fine-tune the air and fuel mixture. The sensor only works when it is very hot, so it has a small built-in heater that warms it up after a cold start. This code means the heater circuit has a fault. Bank 2 is the side of the engine opposite cylinder 1, and it only exists on V-shaped or boxer engines.
Can you drive with P0155?
You can drive normally. When cold the mixture is controlled less precisely and the car uses a little more fuel, so do not leave the repair too long.
How do you clear P0155?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0155 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
