Oxygen sensor before catalytic converter: Notes
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2017 BMW X3, 2016 BMW X3, 2015 BMW X3, 2014 BMW X3, and 2013 BMW X3. However, it is still accessible from the selected car via links, so may be relevant.
The oxygen sensor before catalytic converter is a broadband oxygen sensor (control sensor). The broadband oxygen sensor continuously measures the residual oxygen in the exhaust gas. The fluctuating values of the residual oxygen are sent to the engine control unit as a voltage signal. The engine control corrects the mixture composition by changing the fuel injection. A new addition is the enhanced ADV LSU broadband oxygen sensor (Bosch). LSU stands for "universal oxygen sensor" and ADV for "Advanced".