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.

Real-world scan data

Seen in

305

scans in the past year

Found in

0.1%

of scans

0.1%

of scans that found faults

Appears alongside · share of P2271 scans

P0140in 26.6% of scans

P0300in 25.2% of scans

P0138in 24.9% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P2271 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX