P2271
O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2
Fuel & air metering (O2 sensor)
Generic OBD-II
Medium
What it means
P2271 means the downstream oxygen sensor on bank 1 (behind the catalytic converter) is reporting a signal stuck at a rich value instead of switching normally. It's most often a failed sensor or a wiring/exhaust-leak issue, though a genuinely rich exhaust can also trigger it. The engine typically still runs fine; the main consequences are the warning light and disrupted emissions monitoring.
Medium
Can I keep driving? Generally drivable — this is a downstream oxygen-sensor monitoring fault, so the car runs, but the light stays on and emissions monitoring is affected.
Common symptoms
What you'll notice
- Check-engine light on
- Possible slightly higher fuel consumption
- Occasional rough idle
- Failed emissions test
Common causes
Most likely first
- Failed downstream (bank 1, sensor 2) oxygen sensor stuck at a rich readingLikely
- Open, shorted, or corroded wiring at the sensor connectorCommon
- Exhaust leak near the sensor skewing its readingCommon
- Genuinely rich exhaust from a fuel-system fault (pressure or injectors)Less often
How to diagnose & fix
Work through it in order
- Read the bank 1 sensor 2 voltage live — a signal pinned high with no normal switching points to the sensor or a real rich condition.
- Inspect the sensor connector and wiring for corrosion, damage, or a short.
- Check for exhaust leaks upstream of and around the sensor.
- Rule out an actual rich mixture (fuel pressure, leaking injectors) before condemning the sensor, then replace the O2 sensor if it's at fault. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2271?+
Usually yes. The rear O2 sensor is mainly used to monitor the catalytic converter, so drivability is minimally affected — but confirm the exhaust isn't genuinely running rich.
Can I just clear P2271?+
It will return once the ECM re-checks the sensor unless the stuck signal or its cause is repaired.
Related codes
Often seen with P2271
Read & clear P2271 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