P0155 means O2 Sensor Heater Circuit (Bank 2 Sensor 1). The computer has detected a fault in the heater circuit of the upstream bank 2 oxygen sensor. On a V engine, bank 2 is the side opposite cylinder 1. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0155 means
Oxygen sensors measure the oxygen left in the exhaust. Sensor 1 sits before the catalytic converter and is used for fuel control; sensor 2 sits after it and mainly monitors the converter. Most sensors have a heater so they start working soon after a cold start. A traditional zirconia sensor switches between about 0.1 volt (lean) and 0.9 volt (rich); many newer upstream sensors are wide-band air-fuel sensors that report differently, so check which type your engine uses.
P0155 symptoms
- Check engine light
- Longer time to enter closed-loop fuel control after a cold start
- Little or no drivability change in many cases
Common causes of P0155
- Failed heater element inside the sensor
- Blown fuse or relay feeding the heater
- Damaged wiring or a corroded connector near the exhaust
How to diagnose P0155
- Check the heater fuse
- Measure the heater’s resistance at the sensor connector
- Check for battery voltage to the heater with the key on
- Inspect the harness for melted or chafed wiring
Can you drive with P0155?
Usually yes in the short term; repair before an emissions inspection and to protect fuel economy.
P0155 tips
Some vehicles feed all oxygen sensor heaters from one fuse; if several heater codes set together, check that fuse first.
Will P0155 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0155 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0135 | O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) |
| P0154 | O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1) |
| P0161 | O2 Sensor Heater Circuit (Bank 2 Sensor 2) |
Guides that help
When it is more than a sensor
Oxygen sensor codes are fixed with a sensor, wiring, a fuse or an exhaust leak repair. An engine burning oil or coolant contaminates sensors quickly; if new sensors keep failing, check for blue or white exhaust smoke and a head gasket leak, and compare engines by code on our engines page if the engine is worn out.
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