A Warning Sensor turns the brake warning light on during a hydraulic brake malfunction. If not working, this switch should be serviced or replaced. Damaged lines should be replaced. Cracks can form from temperature variations and aging. Inner surfaces can become clogged.
Leaks can occur at end fittings.
New hoses should be installed for any of these reasons. The frictional contact of the Brake Shoes slows and then stops the drum. As brake shoes wear down from normal usage, cylinder pistons are spaced out farther than usual in the chamber. The debris hampers the free movement of pistons. Corroded wheel cylinders should be replaced.