O2 Sensor Signal Stuck Rich (Bank 1, Sensor 2)
The P2271 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Signal Stuck Rich (Bank 1, Sensor 2). This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- medium
- Estimated cost
- $50-$200 for downstream O2 sensor
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Common Symptoms
- Check Engine Light on
- Catalyst efficiency code may also appear
- No drivability impact
Probable Causes (Ranked by Likelihood)
- Failed downstream O2 sensor stuck at high voltage Very High
- Catalytic converter passing excess fuel (poor efficiency) Moderate
- Wiring fault shorting downstream sensor signal high Low
Step-by-Step Diagnostic Procedure
-
Monitor downstream sensor voltage. Stuck above 0.7V under steady cruise indicates sensor failure or cat passing excess fuel.
-
Compare to upstream sensor behavior. If upstream is normal, focus on downstream sensor and cat.
-
Replace downstream sensor and retest before condemning the catalytic converter.
Common Fixes by Vehicle
What techs usually find when diagnosing P2271 on specific vehicles — tap your vehicle for the fix and the exact part:
2006-2015 Ford Fusion/Escape 2.5L/3.0L easy DIY
P2271 = rear O2 stuck rich. Same fix approach as P2270 but opposite direction. First check for an exhaust leak at the front pipe that's drawing oil or soot past the cat. Then replace the downstream O2 with OE part (Denso/NTK).
Labor: 30 min2004-2013 Chevrolet Impala/Malibu 3.5L/3.9L moderate DIY
Failed catalytic converter saturated with oil or coolant will always read rich downstream. If the cat looks discolored, clogged, or rattles, it's done. Replace with CARB-compliant direct-fit (Walker or Magnaflow) if state emissions-sensitive.
Labor: 2 hours2007-2014 Chevrolet Silverado/Tahoe 5.3L AFM hard DIY
On GM DOD/AFM engines, oil burn through the piston rings saturates the cat and downstream O2. Fix the oil consumption (updated rings/stem seals) before replacing the O2 sensor. Otherwise the new sensor fails quickly.
Labor: 10-20 hours (ring job)Frequently Asked Questions
Should I replace the downstream O2 sensor before the catalytic converter?
Always yes. The downstream O2 sensor is far less expensive ($50-$200) than a catalytic converter ($350-$2,500). A stuck sensor is more likely than a failed cat on vehicles under 150,000 miles. Replace the sensor first and retest.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P2271 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
See All Codes & Fixes for Your Vehicle
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