Fuel & air metering · Powertrain · generic (SAE-defined)
P2271: O2 Sensor Signal Biased/Stuck Rich (Bank 1 Sensor 2)
P2271 means the bank 1 downstream oxygen sensor, after the catalytic converter, keeps reading rich and does not swing lean when the computer reduces fuel.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P2271 sets
The powertrain control module (PCM) may briefly cut fuel, for example during deceleration, and expects the bank 1 sensor 2 signal to drop toward lean. If the signal stays rich, the PCM decides the sensor is biased or stuck rich. Test details are manufacturer-specific.
Common causes of P2271
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Failed or contaminated bank 1 sensor 2 oxygen sensor
- Engine running rich from a fuel delivery fault
- Sensor signal wire shorted to voltage
- Oil or coolant contamination of the sensor
- Leaking fuel injector
P2271 symptoms
- Check engine light on
- Often no drivability symptoms
- Possible fuel odor or reduced economy
- May fail an emissions inspection
How P2271 is diagnosed
- Scan codes and freeze frame; note any upstream rich codes.
- Check fuel trims to see whether the engine runs rich.
- Watch the downstream sensor during a deceleration fuel cut; it should drop lean.
- Inspect sensor wiring for shorts to voltage.
- Check for oil or coolant consumption.
Typical fixes for P2271
- Replace the bank 1 sensor 2 oxygen sensor
- Repair wiring faults
- Fix the cause of a rich mixture
- Repair oil or coolant leaks into the combustion chamber
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P2271 FAQ
What does code P2271 mean?
P2271 means the bank 1 downstream oxygen sensor, after the catalytic converter, keeps reading rich and does not swing lean when the computer reduces fuel. The standard definition is "O2 Sensor Signal Biased/Stuck Rich (Bank 1 Sensor 2)."
Can I drive with a P2271 code?
Generally yes for now, but book a diagnosis. If the engine is truly running rich, prolonged driving can stress the catalytic converter.
Is P2271 common?
It is a fairly common downstream sensor code, often from a sensor that has aged or become contaminated.
Can P2271 come with P0420?
Yes. Both involve the downstream sensor, so a faulty sensor or a rich-running engine can trigger both.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.