O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2
The Powertrain Control Module (PCM) has detected that the downstream oxygen sensor on Bank 1 (Sensor 2) is continuously sending a high voltage signal, indicating a rich exhaust condition. This means the sensor is either failing to toggle properly or the exhaust stream exiting the catalytic converter is genuinely lacking oxygen.
This code typically does not cause immediate drivability issues or strand the vehicle. However, it will cause an emissions test failure and should be diagnosed to prevent potential long-term catalytic converter damage.
Common symptoms
- Illuminated Check Engine Light
- Failed vehicle emissions test
- Slight decrease in fuel efficiency
- Strong exhaust odor (if the engine is genuinely running rich)
- Engine running slightly rough (in rare cases where rear O2 influences fuel trim)
Likely causes
- Faulty Bank 1 Sensor 2 oxygen sensor
- Damaged, melted, or corroded wiring and connectors for the O2 sensor
- Exhaust leak near the downstream oxygen sensor
- Excessively rich engine condition (e.g., leaking fuel injector or high fuel pressure)
- Failing catalytic converter
What to check before replacing parts
Visually inspect the Bank 1 Sensor 2 wiring harness and connector.
Look for: Look for melted wires from exhaust heat, chafing, or corrosion inside the connector pins that could cause a short to voltage.
Monitor the O2 sensor voltage using a scan tool with live data.
Look for: Observe the Bank 1 Sensor 2 voltage; if it remains steadily above 0.8 volts without fluctuating, the sensor is stuck rich.
Induce a temporary lean condition to test sensor responsiveness.
Look for: Create a small, controlled vacuum leak while watching the live data. If the sensor voltage does not drop toward 0.1 volts, the sensor is unresponsive and likely faulty.
Inspect the exhaust system for leaks near the catalytic converter and O2 sensor.
Look for: Listen for ticking sounds or look for black soot marks around exhaust flanges and the sensor bung that could indicate a leak skewing the sensor reading.
Check the engine's fuel trims using a scan tool.
Look for: Look at the short and long-term fuel trims for Bank 1. Highly negative numbers indicate the engine is actually running rich, meaning the sensor is correctly reporting a rich condition caused by another engine fault.
This page explains the generic P2271 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.