Why is My Car's ABS Warning Light On? What to Do Next

If your ABS warning light has come on, it’s not something to ignore. While your car will usually still drive, the light means your anti-lock braking system isn’t working properly, which can seriously affect your safety in an emergency stop.

The light usually means there’s a problem with one or more components of the system, like a faulty wheel speed sensor, damaged wiring or low brake fluid. While your brakes will still work, the safety feature that prevents wheel lock under hard braking might not.

In this guide, you’ll learn what the ABS warning light means, the common causes behind it and what steps you can take to diagnose and fix the issue before it becomes a bigger problem.

What is an anti-lock braking system (ABS)?

An anti-lock braking system (ABS) is a safety feature that prevents your wheels from locking up when you brake hard or on slippery surfaces. It rapidly pulses the brakes to maintain traction so you’re able to steer while slowing down rather than skidding uncontrollably. This makes your vehicle far safer and more stable in emergency braking situations.

ABS was first developed for aircraft in the 1950s, then gradually adapted for road cars in the following decades. By the 1980s and 1990s, it became standard in most modern vehicles as manufacturers recognised how significantly it reduced accident risk.

Today, every new car sold in the UK comes equipped with ABS as part of its mandatory safety systems.

How does ABS work?

Anti-lock braking works by continuously monitoring the speed of each wheel and automatically adjusting brake pressure to prevent any of them from locking up. It uses a series of sensors and valves to apply and release braking force so your car maintains grip and control, even in sudden stops. And this all happens in a fraction of a second.

Here’s a more in-depth breakdown of what’s actually happening inside:

• ABS system components: The system includes wheel speed sensors, valves, a pump and an electronic control unit (ECU). These components work together to monitor wheel speed, adjust pressure, and prevent wheel lock-up under heavy braking.
• Detecting wheel speed: Each wheel has a sensor that tracks its rotation speed. The ECU compares these readings in real time to spot when one or more wheels begin to slow faster than the others (which indicates potential lock-up).
• Modulating brake pressure: When the ECU detects a wheel about to lock, it signals the hydraulic control unit to reduce brake pressure to that wheel through solenoid valves, easing the grip until traction is restored.
• Reapplying brake pressure: Once the wheel starts turning again, the ABS pump reapplies brake pressure in quick bursts. The rapid cycle of release and reapplication happens multiple times per second to maximise braking efficiency while preventing skidding.
• Maintaining steering control: By keeping the wheels turning, ABS makes steering possible even during hard braking. That extra control helps you avoid obstacles and keep the vehicle stable in emergencies and poor weather conditions.

Now… ABS is different from traditional braking systems. Older setups applied constant brake pressure until the wheels stopped turning. This would cause them to lock up and the car would skid.

Without anti-lock braking, that’s exactly what your car would do: it’d be much more likely to skid during hard braking, especially if the road is wet or icy. You’d lose steering control, which would increase your stopping distance and the chances of a collision.

What can cause the ABS warning light to turn on?

The ABS warning light usually activates because the system detects a fault that prevents it from working correctly. The most common causes are a failed wheel speed sensor, damaged wiring, low brake fluid, a blown fuse or a problem with the ABS control module.

Faulty wheel speed sensors

Wheel speed sensors are small magnetic devices located near each wheel or within the hub assembly. They’re constantly monitoring how fast each wheel is turning and send that data to the ABS control unit.

When you brake, the system compares each wheel’s speed. If one slows too quickly (as if it’s about to lock), the ABS reduces pressure to that wheel to keep traction.

If a sensor gets damaged, dirty or fails electrically, it sends incorrect or no data at all. The ABS module interprets this as a system fault and activates the warning light to alert you.

The common signs of wheel speed sensor failure:

• Inconsistent speedometer readings
• Traction control or stability control lights also turning on
• Brakes locking or pulsing unexpectedly during normal driving
• Loss of anti-lock braking during sudden stops

Low brake fluid levels

Brake fluid is vital for the function of both your main braking system and the ABS. It transfers the force from your brake pedal into hydraulic pressure. That pressure is what applies the brakes at each wheel.

When the fluid level drops too low, air enters the hydraulic lines, which reduces pressure and makes the system less effective. The ABS relies on consistent hydraulic pressure to modulate braking, so when that pressure falls, the system can’t operate properly.

The main sign you’re looking for here is if your ABS warning light comes on along with the main brake warning light. You might also notice a spongy brake pedal, longer stopping distances or the pedal sinking lower than usual when pressed.

Malfunctioning ABS control module

The ABS control module is the brain of the anti-lock braking system. It receives data from each wheel speed sensor, analyses it and decides when to adjust brake pressure to prevent wheel lock-up.

When the control module develops a fault from internal electrical failure, corrosion on its connectors or software issues, it can no longer process sensor signals correctly. That means it can’t control the hydraulic valves or pump effectively.

As soon as the system detects poor response from the control module, it triggers the ABS warning light. In a lot of these instances, the standard braking system will still function, but the anti-lock feature that prevents skidding will be disabled.

Worn-out brake pads

As your brake pads wear down over time, they reduce braking efficiency. When that happens, they indirectly affect how the ABS performs.

When brake pads become too thin, the caliper pistons have to extend further to make contact with the discs. This increases the volume of brake fluid needed in the system, which lowers the overall fluid level in the reservoir. If the fluid drops too low, it’ll trigger the ABS warning light (and possibly the main brake warning light as well).

And if the pads are unevenly worn, they’ll cause inconsistent braking pressure across your wheels. The ABS system sometimes detects this imbalance as a potential fault and stores an error code, causing the light to stay on.

Wiring problems or corrosion

The ABS relies on a network of electrical connections linking the wheel speed sensors, control module, and hydraulic unit. If those wires get damaged, frayed or corroded, the signals can’t travel correctly.

Corrosion tends to build up at connectors near the wheel hubs or underbody. That’s where they’re most exposed to moisture, salt and road grime.

Even a small amount of resistance in these circuits might confuse the ABS control unit and trigger the warning light, which is why it’s so important to inspect the wiring and connectors when the light comes on, especially if your car is older or you drive a lot in harsh conditions.

The common signs of ABS wiring issues:

• Intermittent or flickering ABS warning light
• Loss of ABS function only at certain speeds or conditions
• Traction or stability control lights appearing alongside the ABS light
• Physical damage or corrosion that’s visible on wiring near the wheels
• Diagnostic trouble codes (DTCs) related to communication or sensor circuit faults

What to do next when your ABS light turns on?

If you notice your ABS light activate, the first step is to stay calm. Your standard brakes will still work, it’s only the anti-lock function that helps prevent skidding that won’t.

Then, check whether the light is solid or flashing. A solid ABS light means the system has detected a fault, like a dirty sensor or low brake fluid. A flashing one can either mean there’s an active system failure that needs immediate attention, or one that’s intermittent.

Whatever the cause, the one thing that’s for certain is that the ABS system is deactivated. So, this issue demands your immediate attention.

Let’s break down what to do step by step:

Check brake fluid levels.

Again, low brake fluid sometimes triggers the ABS light. Here’s how to check and top it up safely:

1. Park the car on a flat surface and switch off the engine.
2. Open the bonnet and locate the brake fluid reservoir (it’s usually a small, clear plastic container near the back of the engine bay).
3. Check the fluid level and verify it’s somewhere between the “MIN” and “MAX” marks.
4. If it’s low, clean the cap before opening it to avoid contamination.
5. Add the correct brake fluid type (DOT 3, DOT 4 or DOT 5.1; check your owner’s manual) until it reaches the “MAX” line.
6. Replace the cap securely and wipe any spills.

Over time, brake fluid absorbs moisture, which eventually leads to corrosion and reduced braking performance. It’s best to replace it every 2 to 3 years, 30,000 to 45,000 miles or as recommended by your vehicle manufacturer.

Inspect the ABS fuse.

The ABS fuse protects the system’s electrical circuit from damage caused by power surges and short circuits. If it blows, the ABS loses power and the warning light will pop on to let you know the system’s been turned off.

This is how you’ll locate and check the ABS fuse:

1. Turn off the ignition and remove the key.
2. Open the fuse box (you’ll find it under the dashboard or in the engine bay).
3. Use your owner’s manual to find the exact position of the ABS fuse.
4. Carefully remove it using fuse pullers or needle-nose pliers.
5. Hold the fuse up to the light and check the thin metal strip inside. If it’s broken or burnt, it means the fuse has blown.
6. Replace it with one of the same amperage rating (printed on the fuse) and reinsert it securely.

If the new fuse blows again shortly after replacement, it means there’s an underlying electrical fault or short circuit in the ABS wiring or control module. In that case, I’d recommend having the system inspected by a qualified technician before you drive the car again.

Run a diagnostic scan.

A scan tool connects to your car’s onboard computer and retrieves error codes stored by the ABS control module. These codes point directly to the faulty sensor, circuit, or component causing the issue.

How to run a scan using an OBD-II diagnostic tool:

1. Locate the OBD-II port under the dashboard near the steering column.
2. Plug in your diagnostic scanner and turn the ignition to the “ON” position (engine off).
3. Follow the scanner’s on-screen prompts to select the ABS system.
4. Wait for it to read and display the stored trouble codes.
5. Note down the codes or use the scanner’s built-in database to interpret them (don’t delete them, they give important context for the mechanic).

If the scan reveals multiple codes, you’re better off visiting a qualified mechanic. Professional workshops have advanced diagnostic tools that perform live data checks, test individual sensors and confirm whether the fault is mechanical or electrical.

Check for obvious damage or issues.

Identifying visible problems like damaged wiring, broken sensors and leaking fluid early saves time and prevents further damage to the braking system.

To visually inspect your ABS system:

• Park the car safely on level ground and turn off the engine.
• Look behind each wheel to locate the ABS sensor and its wiring (it’s on or near the wheel hub, behind the brake disc).
• Check for frayed or exposed wires, loose connectors and corrosion at the plugs.
• Inspect around the brake lines and master cylinder for fluid leaks or damp patches.
• Examine the wheel hubs for built-up dirt, rust or debris that could interfere with sensor readings.

After you inspect it visually, turn the ignition on (engine off) so the dashboard lights up. Then gently move or tap the wiring near the sensors. If the ABS light flickers while you do this, there’s a loose or damaged connection.

Seek professional help.

If…

• Your ABS warning light stays on after you’ve checked the basics, and/or
• Your diagnosis reveals issues you’re not qualified to handle yourself

…it’s time to take the car to a qualified mechanic. They’ll run a full diagnostic test, pinpoint the exact cause, repair or replace the faulty component and reset the system safely.

Even if the prospect of that sounds a bit daunting at first, you can’t ignore ABS warning light issues. You’ve already lost the anti-lock feature that prevents skidding in an emergency. So your safety (and that of those around you) is significantly compromised if you have to brake hard.

When to consider scrapping your car due to ABS issues

Sometimes, fixing an ABS fault simply isn’t worth it. If the cost of parts and labour outweighs the car’s remaining value, you’re going to have to make some hard decisions about what to do with it.

Here’s when it makes more sense to scrap your vehicle instead of repairing it:

When repair costs outweigh the value of the car

ABS repairs range from simple sensor replacements to full control module or pump replacements, which can cost hundreds of pounds. If your car’s only worth a few hundred more than the repair, the economics don’t add up.

For example, replacing an ABS pump or module can easily exceed £800 to £1,500 once labour is included. On older vehicles, that might be more than the car’s trade or scrap value. In that case, scrapping and using the payout toward a newer, safer car is by far the smarter option.

When ABS failure compromises vehicle safety

If the ABS light has been on for a long time and other braking issues are developing (like spongy pedals, uneven braking or traction control faults), your car’s safety is at significant risk regardless of the ABS system.

Driving without a functioning ABS doesn’t just increase stopping distance; it also reduces steering control in emergencies. If repairs can’t guarantee full safety restoration or are repeatedly failing, it’s time to consider retiring the vehicle.

The financial impact of continuing to repair an older car

Older cars with persistent ABS faults tend to come with other age-related issues like worn suspension and rusted brake lines. Each repair adds up and when you factor in the amount of depreciation that’s already taken place, it’s almost never a good investment.

If your car’s older than 10 years, have the mechanic look at what else you’ll need fixed over the next year or so. When yearly repairs approach or exceed that value, scrapping the car and upgrading to a newer model makes more financial sense.

Scrapping your car is also easier than you think. When you scrap your car with us, we’ll pick it up for free today or tomorrow, handle all the paperwork for you and pay you on the spot.

Preventive tips to keep the ABS light from turning on

Preventing ABS issues is far easier (not to mention cheaper) than repairing them. With a few simple maintenance habits, you’ll be able to keep your braking system in top shape and reduce the chances of that warning light appearing again.

There are five things I’d recommend for every driver in the UK: 

Regular brake system maintenance

Routine checks help you spot small problems like worn seals or corroded connectors while they’re still cheap to fix. That’s why you should have your braking system inspected at least once a year or every 10,000 to 12,000 miles.

A technician will check fluid levels, inspect lines and hoses for leaks and test the performance of both your brakes and ABS.

Monitor and replace worn-out brake pads

Your brake pads wear down gradually with every stop. Once they get too thin, they’ll cause uneven braking pressure and drop the brake fluid level, both of which affect ABS operation. 

It’s best practice to replace them when they’re down to around 3mm of material left. If you hear squealing and grinding noises, that’s also a dead giveaway it’s time. Doing so protects your discs, improves your brakes’ response and keeps the ABS system performing as it should.

Periodic inspection of ABS

Periodically open the fuse box and look for any signs of corrosion, moisture or burnt fuses related to the ABS system. Also look at the visible connectors and wiring looms near the wheel hubs for damage or rust buildup and to make sure everything’s connected securely.

Doing this helps you spot early signs of sensor and wiring problems that might otherwise go unnoticed until the ABS warning light appears.

Keep your ABS system clean and free from debris

Wheel speed sensors sit close to the brake discs and hubs, which means they easily collect dirt, rust and metallic dust over time. Gently cleaning around the sensors during tyre rotations and brake services prevents this buildup, which can interfere with readings.

If you do this yourself, avoid using high-pressure water directly on sensor areas, as that will potentially force moisture into electrical connectors.

Ensure proper tyre maintenance

The system expects all wheels to rotate at similar speeds. That’s why uneven tyre sizes, worn tread and mismatched tyre pressures all can confuse the ABS sensors.

Check your tyre pressure monthly and keep tread depth above the legal minimum of 1.6mm. Rotating tyres regularly also helps because when you maintain consistent wear, you’ll get accurate readings and stable braking performance.