OBD-II code · Powertrain (generic)
P0040 O2 Sensor Signals Swapped Bank 1 Sensor 1/Bank 2 Sensor 1
The pre-cat oxygen sensors of bank 1 and bank 2 appear to be wired the wrong way around — bank 1 reacts when bank 2 should and vice versa. Typically after recent service.
Is it safe to drive with P0040?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySensors swapped after recent replacement
- PossibleWiring harness routed across banks
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.3–1 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Oxygen Sensor B1s1, Oxygen Sensor B2s1, Sensor Wiring
Related codes
- P0041O2 Sensor Signals Swapped Bank 1 Sensor 2/Bank 2 Sensor 2
- P003DA Camshaft Profile Actuator A Control Stuck On Bank 1
- P003EA Camshaft Profile Actuator A Control Performance/Stuck Off Bank 2
- P003FA Camshaft Profile Actuator A Control Stuck On Bank 2
- P0042HO2S Heater Control Circuit Bank 1 Sensor 3
- P0043HO2S Heater Control Circuit Low Bank 1 Sensor 3
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.