OBD-II Code P2271 — What It Means & How to Fix It

What it means

The downstream O2 sensor on Bank 1 is stuck reporting a rich exhaust condition — too much fuel compared to the amount of air.
A healthy sensor should move up and down around a midpoint voltage, so a stuck-high reading means either the sensor has failed or there's a real over-fueling problem.
This code often appears alongside catalyst efficiency codes.

Affected Models

All vehicles 1996+
Common in Toyota and Lexus vehicles
Common in Honda and Acura vehicles
Common in General Motors vehicles
Common in high-mileage vehicles over 100,000 miles

Common Causes

Failed O2 sensor stuck at high voltage output
Engine running rich — too much fuel in the combustion cycle
Leaking fuel injector flooding cylinders with excess fuel
Contaminated sensor from raw fuel or oil in the exhaust
Faulty fuel pressure regulator causing over-fueling

How to Fix It

Use a scan tool to view live data from Bank 1 Sensor 2 — watch voltage.

A downstream sensor stuck above 0.7V constantly, with no dipping, confirms the sensor is not cycling normally.
Check for related rich condition codes — P0172 and P0175 are common companions.

If P0172 is also set, the engine is genuinely running rich and that root cause must be fixed first.
Inspect for signs of fuel fouling: black smoke, smell of raw fuel from exhaust.

Black exhaust smoke and a fuel smell confirm a rich condition — check fuel injectors and fuel pressure regulator.
Check fuel trims — long-term negative fuel trims confirm a rich engine issue.

Long-term fuel trim below -10% means the ECM is actively reducing fuel but can't compensate for the over-fueling.
Replace the downstream O2 sensor if live data shows no voltage fluctuation.

Before replacing, confirm fuel trims are normal — replacing a good sensor won't fix a real rich engine condition.

When to Call a Professional

If fuel trims suggest a genuinely rich engine condition, have a mechanic diagnose the root cause before replacing the sensor.
Diagnosis involves checking fuel trims, injector balance rates, and fuel pressure under various conditions.
Expect $80–$150 for diagnosis; the O2 sensor itself costs $50–$150, while fuel system repairs vary widely.

Frequently Asked Questions

How do I know if it's the sensor or a real rich condition?

Check your fuel trims with a scan tool.
If long-term fuel trim is very negative, the engine is genuinely running rich.
If fuel trims are normal, the sensor itself is likely stuck.

Can this code damage my engine?

A real rich condition long-term can wash oil off cylinder walls.
This leads to increased wear.
Address it promptly.

What cars commonly get P2271?

It can occur on any make or model.
It's more common on higher-mileage vehicles where O2 sensors have worn out.