P2271
O2 Sensor Signal Stuck Rich (Bank 1, Sensor 2)
The downstream oxygen sensor on bank 1 reports a constant rich signal during a forced-lean command. Suggests a failed downstream sensor or a sensor contaminated by oil/coolant from upstream engine wear.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Common causes
Ordered by how often each turns out to be the cause.
- Downstream sensor failed stuck richCommon
- Downstream sensor contaminatedPossible
Parts involved
- Oxygen Sensor Downstream
P2271 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.