The post-cat oxygen sensor is stuck reading rich. It could be the sensor, or the engine genuinely could be running rich.
P2271 — also written P2271, P 2271, 2271 — is the OBD-II code for o2 sensor signal stuck rich (bank 1, sensor 2). Same code, same fix: this page covers every spelling of it.
P2271 is a emissions fault code, typically costing £90–£400 to put right in a UK garage.
What causes P2271?
- Failed rear O2 sensor
- Genuinely rich mixture from a leaking injector
- Contaminated sensor from oil or coolant burning
- Short to voltage in the signal wire
How P2271 is fixed
- Check fuel trims before replacing the sensor
- Replace the rear O2 sensor
- Investigate any injector leak or oil consumption
P2271 repair cost in the UK
Most P2271 repairs land between £90–£400 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Can you drive with P2271?
Yes, but a rich mixture wrecks catalytic converters over time.
Urgency: medium.
What P2271 is telling you
Emissions-related codes exist so the car fails its own internal audit before it fails an MOT. The ECU only knows what its sensors tell it, and a lazy sensor, a chafed wire or a leaking pipe will all read as an emissions problem.
On P2271 specifically — o2 sensor signal stuck rich (bank 1, sensor 2) — the stored code records the moment that check failed, not the moment the part gave up. That gap is why two cars with the same code can need completely different repairs.
How P2271 is diagnosed properly
Each of the known causes is ruled in or out in cost order, cheapest and most likely first. On P2271 that means working through them like this:
- Failed rear O2 sensor — compared against live data and a known-good reference before it is condemned — a sensor reading the wrong thing accurately is a different fault from a dead one.
- Genuinely rich mixture from a leaking injector — found with a smoke test rather than by eye, because the leak that throws the code is usually too small to hear.
- Contaminated sensor from oil or coolant burning — compared against live data and a known-good reference before it is condemned — a sensor reading the wrong thing accurately is a different fault from a dead one.
- Short to voltage in the signal wire — checked with the loom flexed and the engine warm, because a wiring fault that is intermittent when cold shows itself under heat and vibration.
An hour of diagnostic time on P2271 routinely saves more than it costs, because the alternative is buying the most expensive part on that list and hoping.
The repairs that actually clear P2271
- Check fuel trims before replacing the sensor
- Replace the rear O2 sensor
- Investigate any injector leak or oil consumption
After the repair the code is cleared and the car is driven until the relevant readiness monitor completes, rather than handed back as soon as the light goes out. A code that has only been erased will come straight back on the next drive cycle.
What happens if P2271 is ignored
It is drivable in the short term. Left for months, though, the secondary damage is what costs money, and the original cheap cause is still there underneath it.
For reference, P2271 typically lands at £90–£400 all-in at an independent garage in the UK — main-dealer quotes for the same job usually sit above that.
Getting P2271 looked at
Bob's Mechanical Repairs is an independent garage in Birnam, Dunkeld, Perthshire, with 32 years of Bob's experience on the tools. If P2271 is showing on your car, bring the scan results with you — we will read the live data ourselves, tell you which of the causes above it actually is, and price the repair before any work starts.