The pulsing comes from the rapid opening and closing of the valves, which can cycle up to 15 times per second. The controller monitors each wheel individually. Three channel, three sensor ABS are equipped with a speed sensor and valve on each front wheel, with one valve and one sensor in the rear axle for both rear wheels. This system is commonly found on pick-up trucks and provides individual control of the front wheels. One channel, one sensor ABS use one valve to control both rear wheels, and one speed sensor in the rear axle.
ABS systems work differently than traditional brake systems.
Pumping brakes, a technique that allows the wheels to unlock so the vehicle remained on a straight path in traditional braking systems, should not be used. Pumping the brakes could increase the amount of time it takes to stop a vehicle. In an emergency, a driver should apply pressure to the brake pedal, and hold it firmly down to the floor. Don't be alarmed by the pulsing action of the brake pedal and, most important, don't release the pedal because the pulsing action means the ABS is working properly. The jury is still out on whether ABS prevents accidents.