P0155: O2 Sensor Heater Circuit, Bank 2 Sensor 1
P0155 means the car's computer found a problem with the heater inside the upstream oxygen sensor on bank 2. It is not usually urgent, but it raises emissions and fuel use after a cold start and should be repaired.
You can drive, but get it checked soon
The data lists no limp mode for this code, so the car can normally be driven for a short time. Expect higher emissions and fuel consumption after cold starts, and fix it soon so it does not lead to follow-up codes.
What it means
The upstream oxygen sensor (sensor 1) on bank 2 measures how much oxygen is left in the exhaust, and the engine computer uses that to adjust the fuel mixture. Bank 2 is the side of the engine that does not hold cylinder 1. The sensor has a built-in electric heater so it reaches working temperature quickly. P0155 sets when the heater current is outside its expected range or the heater driver voltage does not follow the computer's command. GM, for example, fails this outside 0.3 to 3.1 A, and Ford uses its own limits. With the heater faulty, closed loop (the mode where the computer fine-tunes the mixture using sensor feedback) starts late on bank 2 after a cold start, and the sensor checks are suspended. P0155 is the bank 2 counterpart of P0135. If both codes appear together, a shared fuse or power supply is a likely cause.
Likely causes
- Burnt-out heater element in the sensorVery likely
This is the most common cause, and the fix is to replace the oxygen sensor.
- Faulty fuse or relay in the heater supplyPossible
If the heater gets no power, the circuit reads as failed, and a shared supply can also set P0135.
- Open, corroded or shorted heater wiring or connectorPossible
A break or short in the wiring changes the heater current outside the allowed window.
- Faulty heater driver in the control moduleLess likely
If the module cannot switch the heater properly, the driver voltage will not follow the command.
What you may notice
- Check engine light on
- Higher emissions and fuel consumption after a cold start
- Follow-up codes P0153 or P0154 possible
What to check, cheapest first
- 1Read all stored codes and note whether P0135 is also present. Both together point toward a shared fuse or power supply. · you can do it
- 2Check the fuse and relay that feed the oxygen sensor heaters, and replace any that are blown or faulty. · you can do it
- 3Inspect the bank 2 sensor wiring and connector for damage, corrosion, loose pins or melted insulation. · you can do it
- 4Measure the heater circuit resistance and supply voltage at the sensor connector. · mechanic
- 5Replace the bank 2 upstream oxygen sensor if the heater element is open or out of range. · mechanic
- 6If the sensor, wiring and fuse test fine, check the heater driver in the control module, clear the code and complete a drive cycle to confirm the repair. · mechanic
Related codes
Frequently asked questions
Can I drive with P0155?+
Usually yes for a short time, since limp mode is not listed for this code. Emissions and fuel use rise after cold starts, so have it fixed soon.
Can a loose gas cap cause P0155?+
No. P0155 concerns the oxygen sensor heater circuit, not the fuel system's vapor seal. Look at the sensor, its fuse and its wiring instead.
Will P0155 pass an emissions test?+
Probably not. The check engine light is on and the code is emissions-relevant, so repair it and complete a drive cycle first so the monitors can finish.
Can I fix it myself?+
Often yes. The repair is rated medium difficulty and DIY is possible, with an estimated 0.2 to 2 hours depending on whether it is a fuse or a sensor replacement.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10