P2278O2 Sensor Signals Swapped Bank 1 Sensor 3/Bank 2 Sensor 3
- 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
- P2278 reports that the third oxygen sensors of the two banks are connected the wrong way round, so the ECM reads the bank 1 sensor as if it sat on bank 2 and vice versa. The check changes the exhaust of one bank only, for example by cutting its injectors or feeding air into one exhaust line, and watches which sensor answers. A DaimlerChrysler patent describes this test and the risk for control sensors: crossed sensors push one bank leaner and the other richer until both controllers hit their limits. At the third position the effect is milder, since these sensors mainly watch the catalysts, but faults would be blamed on the wrong bank. No manufacturer documents a test for this code publicly; CARB requires usable secondary sensor output. The usual cause is crossed connectors after repairs.
- What you may notice
- Malfunction indicator lamp on
- Catalyst or sensor codes reported for the wrong bank
- Likely causes
- LikelySensor 3 connectors of both banks plugged in crosswise after a repair
- PossibleHarness routed to the wrong side or pins swapped in a connector
- RareWrong harness, ECM 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.