Final answer:
When the hydraulic brakes fail while driving, the correct course of action would be to pull the emergency brake to stop the vehicle.
Step-by-step explanation:
When the hydraulic brakes fail while driving and the system does not build up pressure, the brake pedal will feel spongy or go to the floor. In such a situation, it is important to take immediate action for safety.
The correct course of action would be to pull the emergency brake to stop the vehicle.
This will activate the independent mechanical braking system, allowing you to bring the vehicle to a stop.