P0155 — O2 Sensor Heater Circuit No Activity Detected (Bank 2 Sensor 1)
Drive with caution — fix soon.
What P0155 means
This code means the engine computer detected no activity from the upstream oxygen sensor on bank 2, so it's getting a flat or dead signal instead of the normal rich-lean switching. It's most often caused by a failed O2 sensor, but bad wiring, a blown fuse, or an exhaust leak can also trigger it. The usual fix is replacing the sensor, and it typically doesn't involve major engine repairs.
Common symptoms
- Check engine light is on
- Reduced fuel economy
- Rough idle or hesitation
- Engine may run rich and smell of fuel
- Sluggish or slightly weaker acceleration
Common causes
- Failed upstream O2 sensor on bank 2
- Open or shorted sensor wiring
- Blown fuse or bad ground in the sensor circuit
- Corroded or loose sensor connector
- Exhaust leak upstream of the sensor
Typical repair cost
$150 – $400
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0155 code?
Usually yes, for a short while. The engine will still run but may use more fuel and feel a little rough. Have it diagnosed within a week or two to protect your catalytic converter.
How much does it cost to fix a P0155 code?
Expect roughly $150 to $400 in most cases. The oxygen sensor and labor make up most of the bill, though a simple wiring or fuse fix can cost less.
Is a P0155 code serious?
It's a moderate issue. It won't usually strand you, but the missing sensor signal forces the computer to guess, which raises emissions and can damage the catalytic converter if left too long.
What does 'no activity detected' mean for P0155?
It means the upstream sensor on bank 2 isn't switching the way a healthy sensor should. Instead of moving back and forth between rich and lean, it's giving a flat signal, which usually points to a dead sensor or a broken circuit.