What is ABS in a car? Anti-lock braking systems explained

What are anti-lock brakes (ABS) and how do they work? We investigate the system that has saved countless lives across the world

ABS is a safety feature fitted to all new cars that sees the brakes automatically disengage and re-engage at very high speed if the system detects that the wheels are skidding. This helps the car regain traction, giving the driver more control, and a greater ability to steer the car out of harm’s way.

ABS meaning

ABS stands for anti-lock braking system, and while the principles behind it were initially applied to aircraft in the 1920s, ABS first started appearing on cars in the 1970s, before becoming widely fitted in the 1980s, first to high-end cars, and later to pretty much everything on the market.

How does ABS work?

An ABS system makes use of a car’s ECU (Electronic Control Unit, or “brain”), which is connected to speed sensors on each wheel.

When one of those sensors returns a speed reading significantly lower than the others, the system assumes that the slower rotating wheel is about to lock, and reacts by releasing braking force before reapplying it in rapid succession – around 15 times a second, until the system determines that traction has been regained.

If an ABS system kicks in when you’re driving you will feel a fast pulsing through the brake pedal, together with the noise of the ABS rapidly pump cycling on and off.

What are the pros and cons of ABS?

ABS was a key driver of vehicle safety, and the pros are that it reduces vehicle skidding and retains steering control for the driver. If you get into a skid in a car without ABS, you won’t be able to steer it if the front wheels ‘lock up’ and skid – unless you apply cadence braking, which is pumping the brake pedal as fast as you can – though this will not be anywhere near as fast as an ABS system can manage.

The advantages ABS offers far outweigh the disadvantages, but on loose road surfaces the system can activate when you don’t want it to, while ABS systems can also be expensive to repair if they malfunction.

Does my car have ABS?

Almost certainly, yes: all new cars sold since 2004 in Europe have to have ABS, and it was standard fitment to a number of cars well ahead of that date; all new Mercedes models sold since 1987 come with ABS, for example.

What does an ABS warning light mean?

Cars with ABS systems have a warning light that should come on then go out every time the car is started. If the light remains on, this indicates a problem with the ABS system, which is likely to have been deactivated as a result. You will still be able to drive the car, but bear in mind there will be no automatic braking assistance should you get into a skid. Your car will also fail its MOT test if the ABS light is on.

A number of issues could be behind an ABS warning light, but common issues include a faulty wheel-speed sensor, a broken ABS pump, or a faulty control module.

You can try turning off then restarting the car to see if this clears the fault, but chances are that if you see an ABS warning light, the car will need the attention of a mechanic, and you should get it booked in with a garage or service centre as soon as possible.