P0155: O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)
Key takeaways
- P0155 means the engine computer saw a problem in the heater circuit of the upstream oxygen sensor on bank 2, not necessarily a bad sensor.
- The car is usually safe to drive; expect slightly worse fuel economy after cold starts and a failed emissions test until it's fixed.
- Check the heater fuse and the wiring and connector before buying a sensor; Ford's bulletin for 2020 Super Duty trucks blames water in the connectors, not the sensors.
- A blown fuse is $0–$20, a wiring repair $100–$250, and a new upstream O2 sensor $150–$400 at a US independent shop.
What P0155 means
The little heater inside the front oxygen sensor on one side of your engine isn’t working, so that sensor is slow to start reading after a cold start.
Scanners call it O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1). Bank 2 is the side of a V engine without cylinder 1, so you’ll only see this code on a V6, V8 or flat engine. Sensor 1 is the upstream sensor, before the catalytic converter. An oxygen sensor only reads accurately when it’s very hot, so it has a built-in electric heater to get there within a minute or so of startup. The engine computer switches that heater on and watches the current it draws. If the current is missing, too low or too high, or the sensor takes too long to warm up, it sets P0155.
The code is about the heater circuit: fuse, wires, connector and heater element. The part of the sensor that measures oxygen may be fine.
Is it safe to drive?
Yes, in most cases. Once the exhaust heats the sensor, the engine runs normally. What you lose is a few minutes of accurate fuel control on that bank after each cold start, so fuel economy dips a little and emissions go up. You will fail an OBD emissions inspection with the light on.
What changes the answer: a flashing check engine light, a rough-running engine, or lean or rich codes alongside it. Then you have more than a heater problem, so get it checked before long drives.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Heater element burned out inside the sensor | Heater resistance open or out of spec at the sensor connector; fuse and power are good | $150–$400 |
| Blown heater fuse | Fuse visibly blown or no power at the connector with key on; often other heater codes too | $0–$20; find the short if it blows again |
| Water, corrosion or damage at the wiring or connector | Wires melted on the exhaust or chafed; green corrosion or water in the plug; code comes and goes | $100–$250 |
| Known connector or software issue on some models | A manufacturer bulletin matches your vehicle and engine | Connector repair $100–$250; software update $100–$200; often $0 under warranty |
What to check first
- Read all the codes. If heater codes for other sensors set too, like P0135 on bank 1 or P0161 downstream, suspect a shared fuse, power feed or connector rather than several bad sensors.
- Check the O2 heater fuse. The owner’s manual fuse chart names it. Replace a blown fuse once; if it blows again, there’s a short to find before driving on.
- Inspect the harness. Follow the bank 2 sensor wire up to its connector. Look for wires resting on the exhaust, a broken clip, or water and green corrosion in the plug.
- Measure the heater. A shop checks heater resistance at the sensor and power and ground at the connector. That separates sensor from wiring in a few minutes.
- Check bulletins. Ford has two bulletins for 2020 F-Super Duty trucks with the 6.2L or 7.3L built on or before June 5, 2020, tracing P0155 and related oxygen sensor codes to water getting into the sensor connectors on the transmission harness. Land Rover has a 2016 bulletin covering a long list of oxygen sensor codes. On those vehicles, ask about the bulletin before buying a sensor.
- Replace the sensor last, then clear the code and drive. The heater test usually runs within the first few minutes after a cold start.
What it costs
The cheap outcome is a fuse, under $20. The common outcome is a new upstream sensor at $150–$400 installed, or a wiring repair at $100–$250 if a wire melted or a connector corroded. It’s rare for this code to run past that. Checking the fuse and harness first costs little and catches the cases where a new sensor wouldn’t help. Not sure which sensor is bank 2 on your engine? Ask our AI mechanic.
Related codes
P0155 often shows with P0135, the same heater circuit on bank 1, and with P0153, the slow-response code a weak heater can cause on this sensor. P0161 is the downstream heater on the same bank. For the whole sensor family, see our O2 sensor check engine light guide.
What owners report to NHTSA
4 complaints filed with NHTSA mention P0155, 2 of them since 2015, across 4 different models. The component owners most often filed it under: vehicle speed control.
Manufacturer service bulletins that name P0155
3 technical service bulletins and manufacturer communications filed with NHTSA mention P0155, from 2 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- FORD F-650 SD (2020), bulletin 10181940: Some 2020 F-Super Duty vehicles equipped with the 6.2L or 7.3L engine built on or before 05-Jun-2020 may exhibit an illuminated malfunction indicator lamp (MIL) with diagnostic trouble codes (DTCs) P0132, P0135, P0138, P…
- FORD F-250 SD (2020), bulletin 10199477: Some 2020 F-Super Duty vehicles equipped with a 6.2L or 7.3L engine, 10R140 transmission, and built on or before 05-Jun-2020 may exhibit an illuminated malfunction indicator lamp (MIL) with diagnostic trouble codes (DTCs…
- LAND ROVER RANGE ROVER (2016), bulletin 10105881: "ISSUE: THE CUSTOMER MAY OBSERVE A MIL IN THE INSTRUMENT CLUSTER RELATING TO THE ENGINE SYSTEM (CHECK ENGINE LIGHT) AND ONE OR MORE CODES STORED IN THE PCM RELATING TO HEATED OXYGEN SENSOR (HO2S) IN THE EXHAUST SYSTEM. T…
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Can I just replace the O2 sensor for P0155?
You can, and on a high-mileage original sensor it's often the answer. But check the fuse and the connector first and measure the heater's resistance if you can. If the fuse is blown, a new sensor alone won't fix it.
Why do I have P0155 and P0135 at the same time?
Two heater codes at once, one per side of the engine, usually point to something they share: a fuse, a power feed or a connector. Two sensor heaters rarely fail on the same day.
Will P0155 hurt my engine or catalytic converter?
Not quickly. Without the heater the sensor takes longer to start reading after a cold start, so the engine runs on a preset, slightly rich mixture for a few extra minutes. Fix it, but it isn't an emergency.
Will P0155 clear itself?
If it was a one-time connector glitch, the light can go out after several good drive cycles. If the heater is open or the fuse is blown, the code comes back within a drive or two after clearing.