P2278 — Oxygen sensor signals are swapped between banks
The engine's oxygen sensors for bank 1 sensor 3 and bank 2 sensor 3 are sending signals that appear swapped. This usually happens due to wiring issues, sensor installation errors, or connector problems. The engine control unit detects inconsistent data from these sensors, which can affect fuel mixture and emissions control.
Common causes
The cause is almost always one of a few things. Here they are — P2278 rarely comes from anything outside this list:
- Incorrect oxygen sensor wiring or connectors swapped
- Faulty oxygen sensors on bank 1 or bank 2
- Damaged or corroded sensor wiring harness
- Previous sensor replacement installed in wrong location
Where to start
In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:
- Inspect and correct oxygen sensor wiring and connectors
- Check sensor placement and swap if installed incorrectly
- Test sensors and replace any faulty units
- Repair or replace damaged wiring harness if needed
That is what holds for P2278 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.
Why TorqFix for your car?
Above is what the code means and why it appears. TorqFix goes further — it gives you specific procedures, torque values, wiring diagrams and pinouts for your exact engine, not generic steps for every car. Real workshop data (127,000+ diagrams, 10,000+ procedures), interpreted by AI in your language.
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Code breakdown
🔧 Related repair procedures
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Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
The same code can mean different things on different makes. Match the meaning to your make before acting on it.
Seen a figure that does not match your manual? Write to us — we correct it and note when. support@torqfix.com
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