P0155 Code: O2 Sensor Heater (B2S1) — Causes & Fix
P0155 means a fault in the heater circuit of the upstream oxygen sensor on bank 2, sensor 1.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $40 – $300
- Time to fix
- 30 minutes – 2 hours
What it means
Causes include a failed heater element, a blown fuse, or wiring/connector faults. P0155 is a generic OBD-II powertrain code defined in the SAE J2012 standard, so it applies to virtually any 1996-or-newer petrol car or light truck regardless of make. Fix the underlying fault, then clear the code with an OBD-II scan tool — it will return if the problem isn't resolved.
Symptoms
- Check engine light on
- Slower closed-loop when cold
- May block emissions readiness
How to fix it
- 1
Check the heater fuse and wiring
1. Confirm the O2 heater fuse. 2. Inspect the bank 2, sensor 1 connector.
- 2
Replace the sensor
1. Test the heater resistance. 2. Replace if open, then clear the code.
Frequently asked questions
Is P0155 urgent?
Drivability is usually fine, but it blocks the emissions monitor from completing, so fix it before an inspection.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.