P2278
O2 Sensor Signals Swapped Bank 1 Sensor 3 / Bank 2 Sensor 3
The PCM detects that the O2 sensor signals from bank 1 sensor 3 and bank 2 sensor 3 are swapped — typically a wiring crossover after sensor replacement.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
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.
- Wiring crossover after sensor replacementCommon
Parts involved
- Oxygen Sensor
P2278 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.