P2271: O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2
What to do
The car will usually drive normally. If a catalytic converter has been diagnosed at the same time, treat that as unproven until this sensor is sorted. And if the engine uses oil or has lost coolant, mention it — residue from either coats these sensors and makes them read rich permanently, so a new sensor will fail the same way unless the consumption is dealt with.
What this code means
The post-catalyst sensor on bank 1 reports rich and will not move. The reasoning, and the warning that the catalyst verdict is unreliable until this is fixed, are at P2270.
One cause is specific to a rear sensor reading permanently rich and is worth naming, because it points away from the sensor entirely: an engine consuming oil or coolant delivers combustion products to the rear sensor continuously, and a sensor coated in the residue reads rich and stops responding. Where a car uses oil noticeably, a replacement sensor will go the same way — so the consumption is the repair and the sensor is a consequence.
A rear sensor pinned rich also tends to be read by the monitor as a catalyst that has stopped working, which is the same expensive misattribution described at P2270.
Likely causes
Start here
- Faulty oxygen sensor · moderate
- Contaminated oxygen sensor element · moderate
Less common
- Excessive oil or coolant consumption · specialist
- Damaged wiring harness · moderate
- Signal wire shorted to the heater circuit · moderate
- Corroded or loose connector · easy
Symptoms
Components involved
Information, not instruction
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Community experience
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