Faulty downstream oxygen sensor (bank 1 sensor 2) that is stuck rich or contaminated; Wiring or connector damage between the sensor and the engine computer, such as chafed wires or corrosion; Exhaust leak before the sensor letting outside air skew the reading, or a leak after the sensor causing a false rich signal; Leaking fuel injector or high fuel pressure causing an actual rich exhaust condition; Failing engine coolant temperature sensor keeping the computer in a rich warm-up mode; Restricted air intake or dirty mass airflow sensor reporting less air than actually enters; Aging catalytic converter that no longer stores oxygen properly, affecting the downstream sensor signal

DTC codes / P22xx · Fuel and air metering (injector circuits) / P2271

P2271O2 Sensor Signal Stuck Rich (Bank 1 Sensor 2)

Q: What does code P2271 mean?

O2 Sensor Signal Stuck Rich (Bank 1 Sensor 2). P2271 means the downstream oxygen sensor on bank 1 is reporting a rich exhaust condition and the engine computer has determined the signal is stuck there rather than responding to normal fuel changes. The computer watches the sensor's voltage over time and flags the code when the reading remains persistently high, indicating a rich mixture or a sensor that can no longer switch.

P2271 means the downstream oxygen sensor on bank 1 is reporting a rich exhaust condition and the engine computer has determined the signal is stuck there rather than responding to normal fuel changes. The computer watches the sensor's voltage over time and flags the code when the reading remains persistently high, indicating a rich mixture or a sensor that can no longer switch.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering (injector circuits)

Symptoms you may notice

Illuminated check engine light, often with no other symptoms besides the warning light
A noticeable drop in fuel economy as the engine runs richer than necessary
Rough idle or stumbling acceleration in some cases
Black sooty exhaust smoke or a strong fuel smell from the tailpipe
Failed emissions inspection due to the stored code and rich condition

Common causes, most likely first

Faulty downstream oxygen sensor (bank 1 sensor 2) that is stuck rich or contaminated
Wiring or connector damage between the sensor and the engine computer, such as chafed wires or corrosion
Exhaust leak before the sensor letting outside air skew the reading, or a leak after the sensor causing a false rich signal
Leaking fuel injector or high fuel pressure causing an actual rich exhaust condition
Failing engine coolant temperature sensor keeping the computer in a rich warm-up mode
Restricted air intake or dirty mass airflow sensor reporting less air than actually enters
Aging catalytic converter that no longer stores oxygen properly, affecting the downstream sensor signal

How to diagnose and fix it

Scan all stored and pending codes and freeze-frame data to confirm P2271 is the primary fault and not a companion to other codes
Inspect the bank 1 sensor 2 wiring harness and connector for damage, corrosion, or loose pins, and repair as needed
Check for exhaust leaks before and after the downstream sensor using a smoke test or listening for ticking
Graph the downstream oxygen sensor voltage on a scan tool to see whether it is truly stuck high or switching normally
Test fuel pressure and inspect injectors for leaks if the exhaust is genuinely rich
Replace the bank 1 sensor 2 oxygen sensor if testing confirms it is stuck or contaminated
Clear codes and perform a road test with a scan tool to verify the sensor switches and the code does not return

What the downstream sensor is really telling you

A downstream oxygen sensor that reads rich can be telling the truth about a leaking injector or high fuel pressure, so replacing the sensor without checking fuel trim and injector balance often leads to a repeat code.
Exhaust leaks between the engine and the downstream sensor pull in outside air and can make the sensor read lean, but leaks after the sensor or a cracked sensor housing can trap a rich sample and set P2271.
A lazy upstream oxygen sensor can cause the computer to overcorrect fuel delivery, driving the downstream sensor rich even though the downstream sensor itself is healthy.
The catalytic converter's oxygen storage capacity affects the downstream signal, so a converter that is aging out can set a stuck-rich code without any sensor fault at all.
Some vehicles set P2271 when the sensor heater circuit is failing intermittently, because a cold sensor cannot switch and reports a fixed rich voltage until it warms up.

Can I keep driving with P2271?

You can usually drive short distances to a repair shop, but avoid heavy acceleration and long trips because a rich condition can overheat the catalytic converter and waste fuel. If the check engine light starts flashing or you notice strong fuel smells, stop driving and have the vehicle towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.