Fuel & air metering · Powertrain · generic (SAE-defined)
P0155: O2 Sensor Heater Circuit (Bank 2 Sensor 1)
P0155 means the heater circuit for the bank 2 upstream oxygen sensor has a fault, so that sensor is slow to reach working temperature after a start.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0155 sets
The bank 2 sensor 1 oxygen (O2) sensor has an internal electric heater controlled or monitored by the powertrain control module (PCM). The PCM checks heater current or control-circuit voltage and sets P0155 when the circuit is open, shorted, or drawing current outside its expected range. Monitoring strategy varies by manufacturer.
Common causes of P0155
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Failed heater element in the bank 2 sensor 1 oxygen sensor
- Blown oxygen sensor heater fuse
- Broken, chafed or shorted heater wiring
- Corroded connector
- PCM heater control fault (rare)
P0155 symptoms
- Check engine light on
- Slightly higher fuel use after cold starts
- Usually no drivability symptoms
How P0155 is diagnosed
- Scan for codes; multiple heater codes suggest a shared fuse or power supply.
- Check the heater fuse.
- Measure heater element resistance at the sensor connector; an open circuit confirms a bad heater.
- Verify battery voltage at the heater supply terminal with the key on.
- Check the PCM control or ground side for continuity.
Typical fixes for P0155
- Replace the bank 2 sensor 1 oxygen sensor
- Replace the fuse and fix the cause of any short
- Repair heater circuit wiring or connector
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Some vehicles report upstream heater faults with P0050-series codes or air-fuel ratio sensor heater codes; definitions can vary by manufacturer; check factory service information.
Related codes & warning lights
P0155 FAQ
What does code P0155 mean?
P0155 means the heater circuit for the bank 2 upstream oxygen sensor has a fault, so that sensor is slow to reach working temperature after a start. The standard definition is "O2 Sensor Heater Circuit (Bank 2 Sensor 1)."
Can I drive with a P0155 code?
Yes, in most cases. Once the exhaust heats the sensor the engine usually runs normally, but emissions are higher after cold starts and an inspection will likely fail.
Is the oxygen sensor heater replaceable separately?
No. The heater is built into the sensor, so a failed heater element means replacing the whole sensor.
Why do bank 1 and bank 2 heater codes show up together?
Both sensors usually share a fuse or power feed. If both set at once, check that common supply before replacing either sensor.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.