The P0040 trouble code indicates that the upstream oxygen sensors have been swapped from one bank to another. This code points to a potential issue with the connection or installation of the oxygen sensors in the vehicle’s exhaust system. The term “upstream” typically refers to the sensors before the catalytic converter.
Upstream Oxygen Sensors Swapped From Bank to Bank
Code symptoms P0040.
1. Increased fuel consumption.
2. Engine may run roughly.
3. Illuminated “Check Engine” or “Service Engine Soon” light on the dashboard.
This code is common in brands such as:: Chevrolet, Renault, Ford, Toyota, Nissan, Mercedes Benz, Honda.
Causes of the code P0040.
1. Incorrect installation of upstream oxygen sensors.
2. Wiring or connector issues within the sensor circuit.
3. Sensor connection mix-up during maintenance or repair work.
Code Solutions P0040.
1. Reinstall the upstream oxygen sensors in their correct positions.
2. Check and repair any damaged wiring or connectors in the sensor circuit.
3. Ensure that the correct sensors are connected to the corresponding banks.