OBD-II Code · Sensors
P2271
HO2S Signal Stuck Rich (Bank 1 Sensor 2)
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$150–$500
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Downstream B1S2 stuck rich.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
- Catalyst code may follow
Likely causes
- Failed sensorMost common
- Coolant/oil contamination
- Failed catalyst
Read the full diagnostic procedureP2271 is the Bank 1 downstream O2 stuck-rich complement to P2270 - the sensor reports voltage pinned above roughly 0.8 V and will not drop when the E…
P2271 is the Bank 1 downstream O2 stuck-rich complement to P2270 - the sensor reports voltage pinned above roughly 0.8 V and will not drop when the ECM commands a lean sweep.
Cheapest-first ladder
- compare upstream and downstream traces under a long deceleration fuel cut, where downstream should fall to under 0.3 V within 5 seconds; if it stays above 0.7 V the sensor is internally contaminated or the catalyst is no longer storing oxygen.
- Caveat: never replace the SCR catalyst on a stuck-rich downstream without confirming oil burn or fuel dilution upstream, because catalyst replacement on this code is the most over-sold repair pattern in diesel emissions work.
Vehicle-specific patterns2011 to 2014 Ford 6.7L Powerstroke set P2271 after oil burn from a known turbo seal failure contaminates the downstream sensor, Ford TSB 14-0086; 200…
- 2011to 2014 Ford 6.7L Powerstroke set P2271 after oil burn from a known turbo seal failure contaminates the downstream sensor, Ford TSB 14-0086;
- 2007to 2012 Mercedes Sprinter OM642 BlueTEC contaminate the downstream O2 from EGR cooler coolant leaks;
- 2011to 2016 Duramax LML throw P2271 when the SCR catalyst is over-dosed with DEF from a sticking dosing valve;
- 2014to 2018 Ram EcoDiesel 3.0L set the code from a failing CCV oil separator pushing oil mist into the exhaust path.
Estimated repair$90 to $1,400.
Look up another code
P2271 — frequently asked
What does a P2271 code mean?
Downstream B1S2 stuck rich.
What causes a P2271 code?
Common causes: Failed sensor; Coolant/oil contamination; Failed catalyst.
What are the symptoms of a P2271 code?
Typical symptoms: Check engine light; Catalyst code may follow.
Is it safe to drive with a P2271 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $150-$500.
How do I diagnose a P2271 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
More free tools