Sounds like the power brake booster is bad. Get it checked out.
air coming out of the brake lines... that is if its a truck. if you aply the parking brake.
Vacuum brake booster is defective or the hose going to the booster is leaking.
it is hissing because there is a vacume leak in the brake booster it will require a new brake booster
Hissing from the brake pedals being push indicates that there is air in the brake system. It also indicates that the brake pads may be wore down and are not able to grab to stop the car.
Faulty Vacuum Brake Booster.
The brake lights.
Probably a faulty brake light switch or the brake light switch is installed incorrectly.
the brake light
By the hissing noise it sounds like you need a new brake booster
Whether or not the brake and/or gas pedals are pressed, how far they are pressed, & for how long.
The power brake booster may be going bad.
Your brake booster is malfunctioning