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P0155: O2 Sensor Heater Circuit (Bank 2 Sensor 1)
Severity: Low Usually safe to keep driving, but get it checked.
What does P0155 mean?
The upstream (sensor 1) oxygen sensor heater on bank 2 has a circuit fault. Bank 2 is the side of a V engine opposite cylinder 1; this code doesn't apply to inline engines with a single bank. The heater warms the sensor so it can start fuel control sooner after a cold start.
Generic OBD-II definition: O2 Sensor Heater Circuit (Bank 2 Sensor 1). Confirm applicability in your vehicle service information.
Common causes
- Heater element failed inside the bank 2 upstream sensor
- Blown heater fuse
- Damaged wiring, often routed near the hot exhaust manifold
- Loose or corroded connector
Symptoms
- Check engine light
- Slightly richer running during warm-up
Can I keep driving with P0155?
Severity: Low Usually safe to keep driving, but get it checked.
If the check engine light is flashing or the car runs badly, stop driving and have it checked.
Typical fixes
- Confirm which side is bank 2 for your engine (the side without cylinder 1)
- Check the fuse and heater power with the key on
- Measure heater resistance
- Replace the sensor if the heater is open