Powertrain, generic (extended)

P2271 O2 Sensor Signal Biased/Stuck Rich (Bank 1, Sensor 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Rear oxygen sensor contaminated by coolant, oil or silicone
Faulty front A/F sensor making the rear sensor look stuck rich
Signal wire chafed against a voltage source

Symptoms

  • Malfunction indicator lamp on
  • Catalyst monitor not completing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–350
Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

oxygen sensor downstreamoxygen sensor upstreamoxygen sensor wiring

Related codes

P2270P2273P2097P0138P013AP2196

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov, fordservicecontent.com.