P2278: O2 Sensor Signals Swapped Bank 1 Sensor 3 / Bank 2 Sensor 3
Standardized SAE J2012 code · P22xx — Fuel & air metering and auxiliary emission controls
What does P2278 mean?
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.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Common causes
- High Wiring crossover after sensor replacement
Likelihood is a general estimate across vehicles; your make and model may differ.
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