Some people call it a pressure differential valve, but a brake warning valve by any other name will still send a signal to your dashboard to light up the brake light if it senses there's a problem in the master cylinder. In other words, the brake warning valve is your eyes and ears inside your vehicle's braking system. If it breaks down, you'll want to replace it right away with a new brake warning valve kit from AutoAnything. Our brake warning valve kits include free shipping and a 1-year lower-price guarantee.