ABS Anti-lock Brakes

What are anti-lock brakes and how do they work?

Long gone are the days when you’d have to pump your brake pedal so your car didn’t skid when braking. The anti-lock braking system (ABS) has made driving safer for years and is installed in all modern cars.

You’ve probably heard of it, but do you know exactly what ABS is and how it works? Find out how your car’s ABS improves your driving and what to do if there’s a problem with your brakes.

In this article:

Brake problems

What are anti-lock brakes?

The anti-lock braking system (ABS) is designed to stop your car from skidding when you brake sharply.

If a car is travelling at speed when the driver brakes hard, the wheels could lock. This can cause the car to lose traction and the driver to lose control of the steering. ABS makes this less likely to happen.

How do anti-lock brakes work?

The wheel hubs of a car with ABS each have a sensor which can tell how how quickly each wheel is rotating and the rate of acceleration and deceleration. It’s often part of the car’s system of Electronic Stability Control (ESC). Not all cars with ABS have this system, but you can’t have ESC without anti-lock brakes.

When the driver brakes sharply, ABS works by sensing when the wheels are about to lock. It then rapidly reduces and increases the braking pressure multiple times per second, applying the optimum pressure.

This allows the wheels to keep moving as the car slows down, instead of locking up. It gives the driver more control over steering and makes the car less likely to skid.

What are the components in the anti-lock braking system?

The ABS is made up of 4 components:

  • Speed sensors - These warn the system when a wheel is about to lock up.
  • Valves - These control how much pressure's in each brake line and can relieve pressure if it’s too high.
  • Pump - If a valve releases pressure in the brake line, the pump can increase the pressure again.
  • Controller - This is a computer in the car which monitors the speed sensors and controls the valves.

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When do anti-lock brakes take effect?

ABS brakes don’t kick in when braking gently under normal conditions. They’ll only kick in when braking sharply, for example if a driver is forced to perform an emergency stop.

You may remember being asked to perform an emergency stop when learning to drive or during your driving test. When performed correctly, the driver feels the brake “judder” which is the ABS kicking in as the brakes rapidly engage and release.

When are anti-lock brakes most effective?

ABS is most effective on dry, solid road surfaces. It helps the driver to brake as quickly as possible while maintaining control of the vehicle. But the system can increase overall stopping distances as it continually releases the brake for tiny intervals.

On slippery conditions like snow and ice, or unstable road surfaces like gravel, anti-lock brakes might not be as effective.

What does the ABS warning light mean?

If any part of the anti-lock braking system isn't working as it should, the ABS warning light will come on. You can check your vehicle handbook to find out which warning light this is and what it means.

If the ABS light comes on it means that the anti-lock brake system isn’t activated. This can affect other systems like stability control and traction control, if your car has them. You’ll also fail your MOT if the ABS light is on.

It’s usually still safe to drive your vehicle when the ABS light comes on, as long as you don’t hear any strange noises from the wheels. But you should take your car to a mechanic as soon as possible to check out the problem.

If you hear any strange noises or are unsure, you can call us out to a breakdown.

Published: 25 September 2020 | Updated: 25 September 2020 | Author: The AA

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