P2277
O2 Sensor Signal Biased/Stuck Rich Bank 2 Sensor 3
Fuel & air metering (oxygen sensor)
Generic OBD-II
Medium
What it means
P2277 means the oxygen sensor on bank 2, sensor 3 is reporting a signal that is stuck or biased toward rich. The ECM relies on this sensor to judge the exhaust mixture, so a fixed-rich reading can throw off fueling and emissions monitoring. It's most often a worn sensor, an exhaust leak, or a wiring fault rather than a serious engine problem.
Medium
Can I keep driving? Usually driveable — the car runs, but fueling and emissions may be off, so fix it before long trips or an emissions test.
Common symptoms
What you'll notice
- Check-engine light on
- Possible rough running or a slight surge
- Reduced fuel economy
- Failed emissions test
Common causes
Most likely first
- Aged or contaminated oxygen sensor (bank 2, sensor 3)Likely
- Exhaust leak near the sensor skewing the readingCommon
- Damaged wiring or a poor connector at the sensorCommon
- A genuinely rich condition (leaking injector, high fuel pressure)Less often
- Faulty PCM/ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame and live O2 data to confirm the sensor is reading fixed-rich.
- Inspect for exhaust leaks upstream of the sensor and check the connector and wiring.
- Rule out an actual rich condition — check fuel pressure and injector operation.
- Replace the oxygen sensor if it stays biased rich after the above check out.
- Clear the code and re-test over a full drive cycle.
FAQ
Quick answers
Is it safe to drive with P2277?+
Short term, usually yes. A biased sensor can worsen fuel economy and emissions, so don't leave it long.
Can I just clear P2277?+
You can, but it comes back within a few drive cycles unless the sensor, wiring, or rich condition is fixed.
Related codes
Often seen with P2277
Read & clear P2277 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX