P0040: Oxygen Sensor Signals Swapped Bank 1 Sensor 1 / Bank 2 Sensor 1
MediumPowertrainO2 Sensors
What does P0040 mean?
P0040 is a diagnostic trouble code indicating "Oxygen Sensor Signals Swapped Bank 1 Sensor 1 / Bank 2 Sensor 1". A sensor in the o2 sensors is reporting abnormal data or has lost communication with the ECU. Sensors can fail due to age, contamination, heat exposure, or wiring issues.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Decreased fuel efficiency
- Rough or irregular idle
- Engine running rough
- Intermittent warning lights
Estimated repair cost
Typical range in Australia (parts + labour)
$200 – $500 AUD
Common causes
- Faulty o2 sensors component
- Wiring or connector issue in the related circuit
- Failed sensor providing incorrect readings
- Software/calibration issue requiring ECU update
- Related component causing secondary fault
What should you do?
Schedule a diagnostic appointment at your earliest convenience. The vehicle is generally safe to drive short distances, but the underlying issue should be addressed to prevent it from worsening.
Get a diagnosis for YOUR car
Code P0040 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.