Why can't the brake pedal of the Audi A6L be pressed down?

[VincentRose]

Audi A6L brake pedal cannot be pressed down possible reasons: caused by wear of the brake master cylinder piston cup or cylinder wall. Solution: the brake master cylinder needs to be replaced. Brake system working principle: the working principle of the brake system is to create huge friction, converting the vehicle's kinetic energy into heat energy. Energy conversion: during acceleration, the car converts chemical energy into heat energy and kinetic energy, and when braking, the brake system converts the car's kinetic energy into heat energy and dissipates it into the air. A car may take 10 seconds to accelerate from standstill to 100 km/h, but braking from 100 km/h to standstill may only take XX seconds, showing that the brake system bears a huge load.