Engine goes off when pressing brake why?

If the engine turns off when pressing the brake, it could be due to a malfunctioning brake switch that is sending a signal to the engine control unit (ECU) to cut off power. Alternatively, it might be a feature in certain vehicles designed to save fuel, such as an automatic start-stop system, which shuts off the engine when the vehicle is stopped. Another possibility is a problem with the ignition system or a vacuum leak affecting engine performance. It's advisable to have the vehicle checked by a mechanic to diagnose the issue accurately.