OBD-II · Engine and powertrain (P)
P2270
Oxygen sensor signal stuck lean bank 1 sensor 2
What it means
The downstream (after the catalytic converter) lambda sensor on bank 1 keeps reporting a lean mixture when the ECU expects it to change. It can be a real lean mixture or a sensor or wiring fault.
Symptoms
- engine warning light
- usually no change in how the car drives
- may fail the emissions part of the roadworthiness test
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | exhaust leak near the downstream sensor (flex pipe, clamps) |
| 02 | aged downstream sensor |
| 03 | genuinely lean running |
| 04 | wiring or connector fault |
What to check, step by step
- 01Fix any fuel-trim, misfire or upstream sensor codes first
- 02Check the exhaust for leaks around the downstream sensor and the flex pipe
- 03Use the OEM enrichment/response test and verify that enrichment reaches the downstream sensor; a brief throttle blip may be buffered by the catalyst.
- 04Check the signal and ground wiring and the connector
- 05Replace the sensor only if it fails the specified response test after mixture, heater and wiring checks.