Number P2271: O2 Sensor Signal Biased/Stuck Rich (Bank 1, Sensor 2)
P2271 is the opposite fault of the same bank 1 rear sensor: its voltage refuses to fall when the exhaust should be lean. It is usually checked during a deceleration fuel cut, when almost pure air passes the sensor. GM's 2018 four-cylinders set it if the signal is still above 100 mV after 25 g of air
Can you drive with P2271?
Severity: Plan the repair. Yes — this is an emissions-system fault. The car will generally drive normally, but it will fail an emissions inspection with the light on.
If you ignore it: Fuel economy and emissions creep up, and some faults in this family (rich/lean running) stress the catalyst over time.
This is the #59 most common code in our top-150 library, in the oxygen & exhaust sensors family (Powertrain system). Severity is Number Nest's editorial triage — if the light is flashing or the car feels unsafe, stop driving it whatever any page says.
What P2271 means
P2271 is the opposite fault of the same bank 1 rear sensor: its voltage refuses to fall when the exhaust should be lean. It is usually checked during a deceleration fuel cut, when almost pure air passes the sensor. GM's 2018 four-cylinders set it if the signal is still above 100 mV after 25 g of air in fuel cut-off (Type B); GM's Bosch-based 2005 V6 looks for a reading above 0.2 V four seconds into the cut, VW's 2014 data books for CC and Tiguan use 0.15 V after 3000 mg of oxygen, and Ford added a fuel-cut stuck test from model year 2019. Causes are a sensor poisoned by coolant, oil or silicone, a signal wire touching voltage, or a front sensor misleading the ECM; Honda traced this on the 2007 to 2008 Acura TSX and replaced both sensors. P2097 and P0138 cover trim and circuit.
Systems involved: oxygen sensor downstream, oxygen sensor upstream, oxygen sensor wiring.
Causes, ranked by likelihood
| # | Cause | Likelihood |
|---|---|---|
| 1 | Rear oxygen sensor contaminated by coolant, oil or silicone | most likely |
| 2 | Faulty front A/F sensor making the rear sensor look stuck rich | possible |
| 3 | Signal wire chafed against a voltage source | less common |
Check them in order — the list is ranked so the likely, cheaper causes come before the expensive part.
Symptoms you may notice
- Malfunction indicator lamp on
- Catalyst monitor not completing
Misdiagnosis traps
- Replacing the part named by the code title without testing. The code reports a failed self-test; the cause list above is ranked so the likely, cheap causes are checked before the expensive part is condemned.
- Clearing the code and declaring victory when the light stays off for a day — the monitor that sets this code runs only under specific driving conditions.
(General diagnostic guidance for this code family — no code-specific trap is published for this code.)
How a good shop confirms it
- Confirm the code and record any companion codes — companions narrow the system fast.
- Inspect the affected components and their wiring/connectors for damage, corrosion and looseness.
- Test the top-ranked cause with live data or a multimeter before replacing anything.
(Standard diagnostic path for this family, labeled as general guidance.)
Repair options & costs
| Repair | Shop total (parts + labor) | DIY (parts only) | Difficulty |
|---|
No single repair is costed for this code — the fix follows the diagnosis. The Repair Cost Estimator prices 28 common repairs once you know which one this is.
OBDex repair data for this code rates the job difficulty medium with a typical labor time in the 0.3–1.5 hour range and DIY possible: yes.
Check the federal emissions warranty first
Before you pay: federal law (the Clean Air Act emissions warranty) requires the manufacturer to cover the catalytic converter and the engine computer (PCM) for 8 years or 80,000 miles on 1995-and-newer cars, whichever comes first. California-emissions (CARB) states cover a longer list of parts for 7 years/70,000 miles, and PZEV-rated vehicles sold in CARB states carry 15-year/150,000-mile emissions coverage on many components. Check your warranty booklet or a dealer lookup before authorizing this repair out of pocket.
Frequently asked questions
How much does it cost to fix P2271?
There is no single fix — the code names a system, and the cost follows whichever cause on the ranked list proves out. The Repair Cost Estimator prices the common repairs in that system; diagnosis (often $100–$180, frequently credited) comes first.
Can I drive with P2271?
See the can-you-drive verdict above — it is based on the system involved and the cascading-damage risk, and it is our editorial triage, not a manufacturer instruction. If the light is flashing or the car feels unsafe, stop driving it regardless of any code.
Will P2271 clear itself?
If the fault was a one-off (a loose cap, a cold-start glitch), the light can go out after several clean trips and the code ages into history. A fault that is still present re-sets the code as soon as the car runs that self-test again — monitors run under specific conditions, which is why "it hasn't come back in two days" is not proof of a fix.
Will my car fail inspection with P2271?
In states with OBD-based emissions inspection, yes — an illuminated check-engine light or an incomplete readiness monitor fails the test regardless of what the tailpipe would show. C-codes (ABS) fall under safety inspection instead in states that have one.
What should I check first for P2271?
The first item on the ranked-causes list above — it is ranked likelihood-first for exactly this reason — plus the free checks: recent work in the area (connectors left loose are a classic), fluid levels, and the battery and grounds on electrical codes.
Where this data comes from
Code facts, causes and symptoms come from OBDex — an open dataset of independently authored descriptions of the standardized generic OBD-II codes (CC0 1.0, public domain; github.com/foerbsnavi/OBDex). The SAE J2012 document itself is copyrighted and is not reproduced here. Cost ranges are Number Nest's own US planning model: national parts and labor ranges cross-checked against the CarMD Vehicle Health Index 2026 published averages, with labor adjustable by the BLS OEWS May 2025 state wage index for auto technicians (occupation 49-3023) — a wage index, not a surveyed shop rate. Severity and can-you-drive notes are our editorial triage, not a manufacturer instruction.