P0040O2 Sensor Signals Swapped Bank 1 Sensor 1/Bank 2 Sensor 1
- 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
- On engines with two exhaust banks, the control module checks whether the upstream oxygen sensors are assigned to the right bank. It changes the mixture on one bank only, actively or as part of normal bank-wise control, and watches which sensor responds. If the sensor that should sit on the other bank reacts, the signals are swapped. This logic is documented for the manufacturer-specific predecessor codes; the usual cause is connectors plugged in crosswise after a repair. If the swap remains, each bank is controlled by the other bank's signal, so fuel trims drift towards their limits.
- What you may notice
- Check engine light on
- Fuel trim and mixture codes possible
- Unstable idle or higher consumption possible
- Likely causes
- LikelySensor connectors plugged in crosswise after a repair
- PossibleHarness routed wrongly or pins swapped in a connector
- RareWrong harness, control module or calibration after a replacement
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €0 – €150
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.