P2278
O2 Sensor Signals Swapped Bank 1 Sensor 3 / Bank 2 Sensor 3
- Severity
- Medium
- Driving
- Drivable — book it in
The signals from the two rearmost oxygen sensors appear to be swapped - bank 1's readings look like bank 2's and the other way round. In practice this almost always means exactly what it says: the connectors have been crossed during previous work.
Possible causes
- CommonSensor connectors crossed during exhaust or sensor replacement
- CommonHarness repaired or extended with the wires transposed
- PossibleWrong sensors fitted for their positions
- PossibleWiring fault making one sensor's signal appear on the other circuit
What you might notice
- Check engine light on
- Fuel trim wrong on both banks
- Failed emissions test
- Fault appearing immediately after exhaust or sensor work
What to check, in order
- Ask what was done recently. If sensors or the exhaust were worked on immediately before this appeared, the connectors are almost certainly crossed.
- Trace each sensor's harness physically from the sensor to its plug rather than assuming the routing.
- Swap the two connectors back and clear the code. If it does not return, that was the fault.
- Check the sensors are the correct part numbers for their positions - some are not interchangeable even when they plug in.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Fuel and air metering - injector circuits
P2200P2201P2202P2203P2204P2205P2206P2207P2208P2209P2210P2211P2212P2213P2214P2215P2216P2217P2218P2219P2220P2221P2222P2223P2224P2225P2226P2227P2228P2229P2230P2231P2232P2233P2234P2235P2236P2237P2238P2239P2240P2241P2242P2243P2244P2245P2246P2247P2248P2249P2250P2251P2252P2253P2254P2255P2256P2257P2258P2259P2260P2261P2262P2263P2264P2265P2266P2267P2268P2269P2270P2271P2272P2273P2274P2275P2276P2277P2278P2279P2280P2281P2282P2283P2284P2285P2286P2287P2288P2289P2290P2291P2292P2293P2294P2295P2296P2297P2298P2299