The function of a proportioning control valve (PCV) in a brake system is to

• ensure that equal pressure is supplied to the front and rear brakes throughout every braking operation
• reduce the brake fluid pressure when the brakes approach their lockup point
• cause less brake fluid pressure to act on the front brakes than on the rear brakes when the fluid pressure exceeds a predetermined level
• cause less brake fluid pressure to act on the rear brakes than on the front brakes when the fluid pressure exceeds a predetermined level.