According to a 2004 study, cars fitted with ABS are 48% less likely to be involved in road traffic accidents than those without. It’s hard to put a number on the number of lives saved, but anyone with experience trying to stop in wet weather in a car without ABS knows how brilliant the technology is.

ABS enables inexperienced drivers to brake safely in wet conditions, with a much reduced risk of losing control or skidding. 

In this article, we’ll discuss how you know your ABS is working and signs it has a fault. We’ll also look at what ABS does and what to do if your ABS is faulty.

How do I know if my ABS is working?

If you recently had to brake very harshly, particularly on a wet or gravelled surface, and you felt the brake pedal and front of the car shake slightly and heard a fast juddering sound, this is your ABS system working.

Why is my ABS light on?

If your ABS light is on, you might have a fault in the system. Here are the four main reasons the light may appear:

• Malfunctioning ABS
• Low fluid reservoir levels
• The system is turned off
• Broken wheel sensors

Signs of ABS failure

Symptoms of an ABS fault are hard to pinpoint. If in any doubt you should always take the car to a mechanic to have the system checked, before continuing to drive. 

Here are three key ABS pump failure symptoms every driver should know.

1. ABS warning light  

The wheel speed sensors are often used by other systems, such as traction control, so the car's ECU constantly monitors the output. If any becomes faulty, the vehicle should display an ABS warning light on the dashboard.

2. Wheels locking up 

One symptom is if your front wheels lock and skid upon hard braking. This can be heard easily if the windows are down but can sometimes be hard to hear in the cabin. The car will feel like it has suddenly hit ice, and the steering will be heavy but unresponsive until the brakes are released.

3. Brake power reduces under hard braking

If the ABS pump fails, braking power can disappear when the ABS activates, often going unnoticed until needed. Given the risks, have the system checked by a professional immediately if you have any concerns.

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What is ABS? 

Before we continue, we’ll quickly recap what ABS means. 

An anti-lock braking system consists of a few key components not found in non-ABS-equipped vehicles. Its basic purpose is to prevent the wheels from locking or skidding under hard braking.

Modern brakes are very powerful. Without ABS, it would be easy for them to lock up the wheels under emergency braking conditions. This is especially important on wet roads.

Why prevent skidding? 

It may seem counterintuitive, but releasing the brakes helps slow the car more effectively than skidding wheels. Steering also only works when wheels are turning, so ABS allows you to brake and steer simultaneously.

Benefits of an ABS system

ABS systems are extremely beneficial to drivers. Here are some key advantages they offer:

• Decrease chances of a frontal collision
• Cars with ABS are less likely to veer off the road
• Fewer fatal crashes
• An overall safer drive

How does ABS work?

The ABS system consists of three main components: an Electronic Control Unit (ECU), an ABS pump/modulator, and ABS sensors. 

All three parts, along with the standard braking system, need to be in good condition for the system to function properly. Here’s a quick breakdown of each.

Electronic Control Unit (ECU)

An Electronic Control Unit is a computer that manages various vehicle functions by processing data from sensors and controlling related components. It oversees tasks like engine management, transmission control, and ABS operation.

ABS Modulator/Pump

The ABS modulator, or ABS pump, is a brake component that rapidly controls brake pressure to prevent wheel lockup. 

It uses a high-pressure pump and valves to adjust braking force in a split second until brakes are released or traction is regained. In many cars, the ECU and pump are integrated into one unit.

Wheel Speed or ABS Sensors

ABS sensors, or wheel speed sensors, are mounted at each wheel behind the brake disc or drum. They detect the spinning ABS ring (reluctor ring) on the drive shaft using a magnetic field, allowing the ECU to monitor wheel speed.

If a wheel locks up during braking, the ECU signals the ABS modulator to adjust brake pressure.

Common causes of ABS failure

ABS can fail prematurely. Because of the relatively low number of parts involved, it is usually easy to diagnose but can be expensive to fix.

1. Wheel Sensor Fault

Common if the car has just had work done on a suspension component, wheel bearing or wheel, the ABS sensors can be fragile devices, and a small knock whilst removing other parts can cause them to send faulty readings. 

An ECU diagnostic check should detect this issue, most cars will also warn of some kind of issue with a general ABS warning on the dashboard. ABS sensors range from £30-£150 each, and would usually take less than an hour to change.

2. ABS pump or modulator fault

An internal ABS pump fault may not always be detectable by software, but cars usually store an error code after a failed ABS attempt. 

ABS modulators can fail due to age or poor brake fluid, which can cause blockages in the valves. Regular brake fluid checks are crucial. 

ABS pumps can be costly, often over £1,000, but refurbishing options might be available. So, always consult your mechanic for advice.

3. Braking system

For the ABS to work effectively, the rest of the conventional braking system needs to be in good working order. 

Common faults with the braking system can be a failed master cylinder, old or insufficient brake fluid, excessively worn pads and discs, seized callipers and more.

How to fix an ABS light

It’s critical to consult a mechanic if your ABS light is on. However, you can also try these at-home checks first.

• Check your car’s manual to locate the ABS fuse box and inspect the fuse for damage. Replacing a faulty fuse might resolve the issue.
• Next, examine the brake fluid reservoir. Low fluid levels can trigger the ABS light, so topping it up with the correct type of fluid may fix the problem.
• If these steps don’t work, dirty or faulty ABS wheel sensors could be the cause. Clean the sensors with a dry cloth to remove debris.
• If the ABS light remains on, consult a qualified mechanic for a proper diagnosis and potential sensor replacement. 

These DIY steps are just initial checks, and if you’re unsure, it's best to seek professional help.

ABS faults - Final thoughts

The ABS is a miracle for modern drivers. Knowing how to check the ABS system is critical, as you want to ensure it’s working properly at all times.

If for any reason, you suspect your ABS, get your car to a garage as soon as possible. They will be able to perform diagnostic checks and ‘field tests’ to see if the ABS is working as it should. 

To find a garage near you enter your vehicle registration and postcode on our website. 

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