ABS warning light on: causes and what to do
The ABS warning light means the anti-lock braking system has detected a fault and disabled itself. Your standard brakes still work, but you have lost the protection ABS provides on slippery surfaces. Here is every cause, what to do next, and UK repair costs.
Normal brakes still work
Your standard braking is unaffected. However, ABS is disabled, so in a heavy stop on a wet or icy road your wheels may lock up. Drive more cautiously, increase your following distance, and book a repair promptly.
Faulty wheel speed sensor
Book a garage soonThe ABS system uses a wheel speed sensor at each wheel to detect how fast each wheel is rotating. When one sensor fails or sends an incorrect signal, the ABS control unit loses confidence in the wheel speed data and disables the ABS system, illuminating the warning light. Wheel speed sensors are the most common single cause of an ABS light. They sit close to the wheel hub and brake disc, exposing them to road debris, brake dust, water, and corrosion. On high-mileage vehicles, the sensor body or the tone ring (a toothed ring the sensor reads) can corrode or crack. A faulty sensor does not affect your standard braking in dry conditions, but it removes the safety net of ABS in an emergency stop.
Symptoms:
ABS warning light on (sometimes with traction control or stability control lights also illuminated), no change to normal braking feel, occasional ABS activating unexpectedly at low speeds just before stopping.
Typical repair cost: Wheel speed sensor replacement: £60 to £180 including parts and labour, per wheel.
Do now: Book a diagnostic scan to identify which sensor has failed. Do not ignore the light: your normal brakes work, but ABS is inactive and will not intervene in an emergency stop on a slippery surface. Avoid harsh braking in wet or icy conditions until repaired.
Damaged ABS reluctor ring (tone ring)
Book a garage soonThe reluctor ring (also called the tone ring or trigger wheel) is a toothed ring that the wheel speed sensor reads as it passes. On older vehicles, the tone ring is a separate component pressed onto the hub or axle shaft. On many modern vehicles, it is integrated into the wheel bearing hub. Corrosion, physical damage from road debris, or cracks in the ring interrupt the signal pattern the sensor receives, causing the ABS system to register a fault. A damaged reluctor ring often produces the same diagnostic fault code as a bad sensor, so the ring must be inspected before replacing a sensor that may otherwise be serviceable.
Symptoms:
ABS light on, possibly with traction control light, fault code pointing to a specific wheel circuit, no abnormal brake pedal feel.
Typical repair cost: Reluctor ring replacement (separate ring): £80 to £200. If integrated into the wheel bearing: wheel bearing and hub assembly replacement, £150 to £400 per wheel.
Do now: Have the sensor and tone ring inspected together. If the ring is corroded or damaged, replacing only the sensor will not resolve the fault. A brake specialist or independent garage can usually identify this on the ramp.
ABS fuse blown
Investigate promptlyThe ABS system is protected by one or more fuses in the vehicle fuse box. If the ABS fuse blows, the entire system loses power and the ABS warning light illuminates immediately. A blown ABS fuse is sometimes the result of a wiring fault elsewhere in the ABS circuit rather than the fuse failing on its own. Replacing the fuse without investigating the underlying cause often results in the new fuse blowing again. The fuse box location and the ABS fuse rating are listed in the owner's manual. Checking and replacing a fuse is a quick and cheap first step before spending on sensors or modules.
Symptoms:
ABS warning light on, possibly alongside traction control and stability control lights, no other braking symptoms.
Typical repair cost: ABS fuse replacement: under £5. If a wiring fault caused the fuse to blow, diagnosis and repair: £60 to £200.
Do now: Check the fuse box and inspect the ABS fuse. If it has blown, replace it and monitor whether it blows again. If it blows again immediately or shortly after, there is a wiring short circuit in the ABS system that requires professional diagnosis.
Failing ABS control module (ABS ECU)
Book a garageThe ABS control module is the electronic brain of the ABS system. It receives signals from all four wheel speed sensors, calculates whether any wheel is about to lock up, and controls the hydraulic ABS pump and solenoid valves to modulate brake pressure. If the module itself fails, the ABS system shuts down entirely and the warning light illuminates. Module failures are less common than sensor failures but more expensive to fix. Causes include water ingress, voltage spikes, vibration damage, or simply age on high-mileage vehicles. On some models, the ABS module can be reprogrammed or remanufactured rather than replaced new.
Symptoms:
ABS light on with no specific wheel-circuit fault code (or multiple codes at once), ABS and traction control both disabled, occasionally accompanied by unusual brake pedal behaviour.
Typical repair cost: ABS module repair or remanufacture: £150 to £400. New ABS module replacement: £300 to £900 including programming.
Do now: Have the ABS system scanned. If fault codes point to multiple circuits or the module itself, seek a specialist in ABS module repair before buying a new unit. Remanufactured modules are often half the price of new and carry a warranty.
Low brake fluid level
Check immediatelySome vehicles illuminate the ABS warning light when the brake fluid level drops below the minimum mark in the reservoir. Low brake fluid can indicate worn brake pads (as pads wear, the caliper pistons extend further and the reservoir level drops), a brake fluid leak, or a failing brake caliper. If the brake fluid level is very low, the ABS hydraulic unit may also be affected. Critically, if the brake fluid is low because of a leak in the brake circuit (not just low pad wear), this is a serious safety issue that requires immediate attention: your braking ability may be compromised beyond just ABS.
Symptoms:
ABS warning light on (sometimes with brake warning light), spongy or soft brake pedal, low fluid visible in the reservoir under the bonnet.
Typical repair cost: Brake fluid top-up: £10 to £30. If caused by worn pads: £80 to £200 per axle. If caused by a leak: £80 to £500 depending on the source.
Do now: Check the brake fluid level under the bonnet immediately. If it is at or near minimum and pads are worn, this is normal. If the level is very low with no obvious pad wear, suspect a leak and do not drive until inspected. A spongy pedal alongside low fluid is a sign of a brake circuit fault requiring immediate repair.
Wiring fault or corroded connector in the ABS circuit
ModerateThe ABS system relies on clean, low-resistance wiring between each wheel speed sensor and the ABS module. Corroded connectors at the sensor, chafed wiring under the vehicle, or a broken wire in the harness (often at a flex point near the steering knuckle or suspension arm) can interrupt the signal and trigger the ABS light. This type of fault often appears intermittently: the light comes on when the car flexes at speed or when damp, then clears. It tends to be misdiagnosed as a sensor failure because the fault code points to the same wheel circuit.
Symptoms:
ABS warning light that is intermittent or clears after driving for a while, fault code pointing to one wheel circuit despite a new sensor being fitted, visible corrosion or damage at wheel speed sensor connectors.
Typical repair cost: Wiring diagnosis and repair: £60 to £200 depending on the extent of the damage. Connector replacement: £20 to £80.
Do now: If an ABS sensor has been replaced and the same fault code returns, inspect the wiring harness and connector at that wheel before replacing the sensor again. A voltage-drop test on the sensor wiring confirms whether resistance is too high.
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Frequently asked questions
Can I drive with the ABS warning light on?
Yes, but with caution. When the ABS light is on, your standard brakes still work normally. The ABS system itself has been disabled, which means in an emergency stop on a wet or slippery surface, your wheels can lock up and you will not have the anti-lock modulation that normally maintains steering control during heavy braking. Drive more cautiously than usual, increase your following distance, and avoid harsh braking. Book a repair as soon as possible rather than driving for weeks or months without ABS.
What does the ABS warning light look like?
The ABS warning light is typically an amber or yellow indicator that shows the letters ABS, sometimes enclosed in a circle. On some vehicles it appears alongside a brake warning light. It should not be confused with the red brake warning light, which indicates a problem with the brake system itself (low fluid, handbrake not released, or a brake circuit fault). ABS lights are almost always amber; brake system warnings are almost always red.
Why are my ABS and traction control lights both on?
The ABS and traction control systems share wheel speed sensor data and often share part of the control module. When the ABS system detects a fault, it disables itself, and because traction control depends on the same data, it is often also disabled automatically. Both warning lights illuminating together almost always points to an ABS fault (most commonly a wheel speed sensor) rather than two separate problems. Fix the underlying ABS fault and both lights will typically clear together.
How much does it cost to fix an ABS warning light?
The most common cause, a wheel speed sensor, costs £60 to £180 to replace per wheel. An ABS reluctor ring (if separate from the bearing) is £80 to £200. A blown ABS fuse is under £5. An ABS module repair or remanufacture runs £150 to £400. If you are having the fault diagnosed before repair, most garages charge £40 to £80 for a diagnostic scan. Getting a diagnostic first avoids guessing and replacing parts unnecessarily.
Can the ABS light come on after fitting new brake pads or discs?
Occasionally, yes. If a wheel speed sensor was disturbed or a connector was damaged during a brake job, the ABS light can come on immediately after. Also, if the sensor wiring was already marginal before the work and the technician removed a wheel without noticing, the additional disturbance can trigger the fault. Inform the garage that the light came on immediately after their work so they can re-inspect without charging for a new diagnostic.
Will the ABS light fail my MOT?
Yes. An illuminated ABS warning light is an automatic MOT failure for cars first used on or after 1 January 2012. For older vehicles, it may be assessed differently depending on whether ABS was originally fitted. The MOT tester checks that all warning lights function correctly and that none relating to a safety system are illuminated at the end of the test. An ABS light on at the end of the MOT is a clear fail.