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January \| February 2004 Volume 78 Issue 1

Feature Article

Antilock Braking Systems—
The ABCs about ABS

Even as experienced drivers, we often know more about how to go than we do about how to stop.

With standard brakes, a slam-on-the-brakes panic stop or a short stop on a wet, slippery road may cause the wheels to lock or skid. The driver loses steering control and the vehicle moves where momentum takes it.

With ABS you should not pump the brakes, you should apply firm pressure because ABS technology prevents the wheels from locking up during hard braking, possibly allowing the driver to steer around a hazard if a complete stop cannot be achieved in time. This control may help the driver avoid a crash or lessen its severity.

The antilock braking system is a computerized system that works in coordination with wheel-speed sensors and the regular brake system on a vehicle. By monitoring the wheel speed during breaking, the computer can detect if one wheel is slowing too quickly. The system then activates a series of valves and pumps to adjust the brake pressure hundreds of times a second. This lowers the brake pressure so the wheel can begin turning again.

Most newer car models offer ABS as either standard or optional equipment. Typically, an ABS indicator light will illuminate on a vehicle’s instrument panel once you turn on the ignition. Many pickups and sport utility vehicles have rear-wheel-only ABS. This prevents the rear wheels from locking up and helps keep the vehicle from spinning out of control. However, if the front wheels lock up, the driver will lose steering control. ABS for cars and minivans are typically designed to keep all four wheels from locking up. An antilock braking system is speed-sensitive and will not activate at very slow speeds. This and other details about the operation and benefits of your system are explained in the vehicle’s owner’s manual.

One way to familiarize yourself with the operation of ABS is to test-drive the vehicle at a speed that allows the ABS to activate, usually above 10 mph. A quiet, empty parking lot is a good place to practice hard braking, so you can experience how the system operates. On wet, slippery surfaces, the lack of traction makes it easier for the brakes to slow the wheel speed, thereby activating ABS more quickly.

If you have any experience with ABS, you know that as you hold down the brakes you can actually feel the vibration in the brake pedal as a result of the repeated brake-pressure adjustment. The valves in the ABS controller may make a grinding or buzzing noise. It is important to be prepared to hear the noise and feel the pulsations so that you won’t react by taking your foot off the brake. You must continue to apply firm pressure, and don’t pump the brake.

The value of ABS lies in its ability to help the driver maintain control of the vehicle during emergency braking situations. ABS may shorten stopping distances on wet or slippery roads, and many systems will shorten stopping distances on dry roads. However, ABS may actually lengthen stopping distances on soft surfaces, such as loose gravel or unpacked snow.

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