Antilock Brakes: Of What Benefit Are They?

By Karen Johnston February 18, 2017

Quick facts

ABS prevents wheel lockup by rapidly modulating brake pressure, up to 15 times per second
On loose surfaces (gravel, snow), ABS may increase stopping distance slightly while preserving steering control
The ABS warning light means the ABS system is disabled. Standard brakes still work, but anti-lock function does not.
ABS wheel speed sensors are a common failure point; they are also used by traction control and stability systems

The anti-lock braking system, or ABS system, is a safety system which prevents the wheels on a vehicle from locking up in a panic stop braking condition, or if you are on a slick surface.

The theory behind ABS brakes is simple. A skidding wheel has less traction than a non-skidding wheel. By keeping the wheels from skidding when you slow down, ABS brakes benefit you in two ways: you will stop faster and you will be able to steer while stopping.

There are four main components to an ABS system: the speed sensors, the pump, the valves and the controller. The speed sensors are located either at each wheel or in the differential. They provide the information that the wheel is about to lock up. The valves are located in each brake line and they pass through, stop and release the brake fluid from the master cylinder to activate the ABS system. The controller is the computer in the car. It watches the speed sensors and controls the valves.

When the ABS is at work you will feel a pulsing in the brake pedal, which comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second. This equates to 60 up to 100 pumping actions per wheel revolution.

Antilock brakes, when used properly, really do help you stop better. They prevent wheels from locking up and provide the shortest stopping distance on slippery surfaces. Properly operating the brakes is a definite factor though, and you should not pump the brake pedal on a car with ABS. The ABS controller has the valves open and close while the pump adds pressure so that the brake pedal pumps for you.

There is really no maintenance or service that is needed with the ABS system. When the ABS light illuminates on your dash the ABS system has been disabled because there is an error in the system. We recommend having that diagnosed and repaired if that light comes on.

Being able to stop and steer your vehicle in a slippery or skidding situation is the main benefit of the ABS system.

Frequently asked questions

Common questions

Should I pump the brakes if my car has ABS?

No. Pumping the brakes is a technique from the pre-ABS era, where rapid pumping prevented the wheels from locking. ABS does this automatically and far faster than a driver can. With ABS, the correct technique in an emergency stop is to apply firm, continuous pressure to the brake pedal and steer around the obstacle. The system will modulate brake pressure at each wheel independently. Pumping the brakes on an ABS-equipped vehicle interrupts the system and reduces its effectiveness.

What causes the ABS light to come on?

The most common cause is a failed wheel speed sensor, which feeds real-time wheel speed data to the ABS control module. Damage to the sensor wiring, a corroded connector, or a failed tone ring on the axle can all trigger the ABS light. The ABS module itself can also fail. When the ABS light is on, the anti-lock function is disabled and the vehicle will use standard braking only. The traction control and stability control warning lights often illuminate at the same time, since those systems share the wheel speed sensor data.

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