P2271

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 patterns: 2011 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; 2007 to 2012 Mercedes Sprinter OM642 BlueTEC contaminate the downstream O2 from EGR cooler coolant leaks; 2011 to 2016 Duramax LML throw P2271 when the SCR catalyst is over-dosed with DEF from a sticking dosing valve; 2014 to 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.