Some indications that the brake master cylinder on a vehicle has gone out include leaking brake fluid under the car or around the brake pedal, and a soft or sluggish brake pedal. In a vehicle that has a brake warning light, the light may also go on.
The brake master cylinder is the part of a vehicle's brake system that directs brake fluid to the braking unit. When the cylinder malfunctions or fails, the brake fluid is no longer directed efficiently. This can lead to brakes that are slow to respond or a brake pedal that can be pressed all the way to the floor without slowing the vehicle.