OBD-II code family
Oxygen Sensor Signal Routing Faults (3 codes)
3 related fault descriptions. Use each full code and the exact vehicle service information to identify its circuit, monitored condition, and required tests.
Codes in this family
This is the complete published member list for this guide. Each code retains its own page; shared diagnostic context does not mean that every member has the same test or repair.
What these codes mean
P0040 concerns the stated Bank 1/Bank 2 Sensor 1 signal-routing condition; P0041 concerns Sensor 2, and P2278 concerns Sensor 3. These three entries preserve both sensor number and bank. Every full code and title remains listed. The designation is not a sensor replacement count, proof of two serial catalysts or a universal physical connector arrangement.
Identify the reporting controller and the exact exhaust and connector layout. Recent sensor, engine or exhaust work is useful history, but does not prove that plugs were crossed. The controller observes signal behavior; the generic label does not provide a physical connector inspection or rule out other signal faults.
Audi’s covered P0040 table uses opposing lambda-control behavior as its monitored criterion. It is not a universal connector-swap test or an instruction to reproduce mixture extremes. Other manufacturers and P0041 require their own procedure. Bank position, sensor type and electrical compatibility cannot be inferred from apparently matching connectors.
Compare routing, part identification and signal attribution using the correct diagram and approved diagnostic checks. Do not exchange bank connectors to see what happens, splice wires from color alone or assume a matching part number makes every swap safe. Heater and signal circuits need separate identification.
Correct only the demonstrated routing, connection or component fault, then verify the affected signals and monitor. Do not quote two new sensors solely because both banks appear in the description.
The Sensor 3 entry likewise reports monitored signal attribution rather than independently proving crossed plugs. A matching part number or apparent opposite-bank response is not a universal swap test or proof that every sensor, heater and circuit is healthy. Preserve related codes, status and repair history, then have the exact protected routing and response checks establish the fault. Follow actual warnings; a stored routing code does not guarantee normal fuel control or safe continued travel.
Identify the circuit on your vehicle
Match the full DTC, reporting module, and any failure-type suffix to the service information for your exact year, make, model, engine, and equipment. An identifier alone does not establish installed hardware count, location, connector pinout, or a universal measurement.
Where the manufacturer publishes its own meaning for this code, that is the one to work from — it describes the actual component on your vehicle, which the generic definition cannot. Keep the generic description for what it is good for: it tells you which subject area the standard assigned the code to, which is useful context when the two appear to disagree. If they do disagree, follow the manufacturer.