P2270O2 Sensor Signal Biased/Stuck Lean (Bank 1, Sensor 2)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2270 concerns the oxygen sensor behind the catalyst on bank 1. When the mixture turns rich, this sensor should rise to a high voltage; if it stays low, the ECM treats it as biased or stuck lean and can no longer rely on it for catalyst monitoring or the post-catalyst trim. GM's 2018 four-cylinders add fuel during a coast-down and set the code if the signal is still under 760 mV once 55 g of air have passed (Type B, two trips); Ford fails a sensor whose highest voltage stays under 0.42 V. P2096 reports the trim correction, P0136 a sensor without activity. Documented triggers include oil on the sensor (Honda Pilot 2023 to 2025), an oil-soaked connector (Mazda CX-9), a bent terminal (GM 2013 trucks) and ECM software (Subaru WRX 2015 to 2016, Forester turbo).
- What you may notice
- Malfunction indicator lamp on
- Catalyst and oxygen sensor readiness not completing
- Usually no noticeable change in driveability
- Likely causes
- LikelyRear oxygen sensor aged, contaminated or slow to reach rich voltage
- PossibleExhaust leak ahead of the rear sensor diluting the gas with air
- PossibleOil in the sensor connector or a bent terminal
- RareCalibration issue fixed by an ECM update
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €0 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.