BMW Repair: button, o2 sensors, compressor operation

Question
whats the button at the bottom of the gas pedal of a  light blue 97 bmw 318i do?  

Answer
Sergio are you speaking about the detent as you fully depress the gas pedal? If you are talking the click you feel at the bottom of the travel then this is the full throttle switch for the engine computer and trans computer. It signals the engine computer to stop using O2 sensors and output maximum fuel and cut a/c compressor operation. The trans computer downshifts.
-Evan