Anti-lock braking systems (ABS) explained

What are anti-lock brakes?

Anti-lock brakes do exactly what it says on the tin; their job is to stop your wheels from locking when you apply the brakes too quickly or too harshly. This allows you to maintain traction, keep control of the steering and avoid skidding, even at high speeds, on hazardous roads, or in poor driving conditions.

How does an ABS work?

An ABS comprises one sensor on each wheel. These sensors work together with your car’s electronic control unit (ECU) and hydraulic pumps. They monitor how quickly the wheels are spinning and relay this information to the ECU.

If one wheel starts to slow down more than the others whilst braking, the ECU assumes it’s about to lock and adjusts the brake pressure accordingly using the hydraulic pumps, sometimes releasing and reapplying the pressure multiple times.

A brief history of ABS

The earliest anti-lock braking system dates right back to the early 20th century. There were several variations developed for trains and aircraft, including one designed by aviation pioneer Gabriel Voisin in 1920.

However, it wasn’t until the 1950s when Dunlop developed the Maxaret anti-skid system that the ABS became widespread in the aviation industry.

Electronic variants were incorporated into car designs in the 1970s and 1980s. They were properly introduced with the luxurious 1978 Mercedes-Benz W116. From here on, more and more carmakers started implementing ABS systems.

In 2004, EU legislation was passed making it mandatory for all new cars to have ABS fitted.

The benefits of ABS

• If you need to make an emergency stop, an ABS will reduce your risk of having an accident by allowing you to maintain control of your car and avoid skidding.

• An ABS can also improve handling. When your wheels are locked, it becomes difficult to maintain control of the steering. With an ABS, you’re still in charge of the direction the wheels turn, no matter what the braking scenario.

• Finally, an ABS will help you retain control of the car in a wide array of weather conditions. For instance, it will be much easier to stay in control if you need to brake on wet or slippery surfaces.

The problems with ABS

Whilst anti-lock braking undoubtedly improves the safety of modern cars, it’s not without its problems. For example, it doesn’t typically work as well on loose road surfaces, which can lead to increased stopping distances.

Repairing a faulty ABS can also be expensive, especially if components such as sensors or hydraulic pumps are damaged.

How to use anti-lock braking systems

An ABS will engage when you press your foot down on the brake pedal firmly with your right foot. It’s important not to press too lightly or to pump the brake.

You’ll probably feel some vibration coming from the pedal but keep pressing it until your car has stopped. Remember you’ve got full control of the steering, so concentrate on that and let the ABS do its thing.

ABS warning light

If the ABS warning light on your dashboard remains lit, there are a couple of things you can do:

Check whether your brake fluid needs topping up. If that doesn’t help, you’ll need to take your car to a garage and get it looked at professionally.

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• Faulty wheel sensors.

• Worn brake pads.

• Broken hydraulic pumps.

• Issues with the ECU.

It’s important to get your ABS fixed, not just so you can be safe on the road, but because a faulty ABS could cause you to fail your MOT.

ABS vs traditional brakes

An ABS and traditional brakes both work in the same way: by applying pressure to the wheels to slow the car down.

The key distinction is that an ABS is an automatic system that’s controlled by a computer, whilst with traditional brakes, it’s up to you as the driver to sense when to brake and apply the correct amount of pressure.

The other difference is that it’s almost impossible for the wheels on car with an ABS to lock. Meanwhile, if the driver of a car without an ABS hits the brakes too hard and too fast, that’s exactly what’s going to happen. An ABS is a much safer option, as it doesn’t rely as heavily on human senses and reaction times.

When are anti-lock brakes most effective?

Anti-lock brakes are most effective when applied firmly and promptly on dry, solid surfaces, and when the vehicle has good contact with the road. For your ABS to work well, the tyres should also be properly inflated and in good overall condition.

When are anti-lock brakes least effective?

Anti-lock brakes are less effective when road contact is poor - and on surfaces such as mud, snow and gravel. However, so long as the tyres and the rest of the vehicle are in good working order, your ABS should still provide enhanced braking control in these conditions.