ABS Warning Light: What It Means and What to Do

What ABS actually does

Anti-lock braking stops a wheel locking when you brake hard or on a slippery surface, by rapidly releasing and reapplying pressure. That lets you keep some steering control while braking firmly. The system relies on a sensor at each wheel that reports wheel speed to a control unit.

When that unit spots a signal that does not make sense, it switches ABS off and turns on the warning light. Often traction control and stability control rely on the same sensors, so those lights may come on too.

Are the brakes still working?

In most cases yes. With the ABS light on alone, the normal hydraulic brakes continue to operate as they would on a car without ABS. What you lose is the anti-lock safety net, so the wheels can lock under hard braking, especially on wet, icy or gritted roads.

Drive more carefully, leave larger gaps and brake earlier. But if the red brake warning light is on, either alone or together with the ABS light, or the pedal feels wrong, stop driving and get the car checked. That suggests a problem with the main braking system, not just the ABS.

If you drive a van for work, think about the load as well. A loaded van with no ABS takes longer to stop and is easier to lock up, so allow for that until the fault is dealt with.

Common causes

The most frequent culprit is a wheel speed sensor. These sit close to the wheel hub, in a harsh environment of dirt, water, brake dust and road salt. They can fail, get contaminated or have damaged wiring. The toothed ring they read, sometimes called a tone ring or reluctor, can also rust or crack.

Other causes include a failing wheel bearing that disturbs the sensor signal, low brake fluid, a faulty ABS pump or control module, a low battery voltage and blown fuses. Salt and damp can be tough on this part of a car, and winter driving on gritted roads is a typical trigger.

It also helps to note whether the light came on suddenly or flickers on and off, and whether it appeared after driving through deep water, after a tyre change or after other work on the car. A light that comes and goes often suggests a loose connector or a damaged wire.

• Wheel speed sensor fault or dirty sensor tip
• Damaged or corroded sensor wiring and connectors
• Cracked or rusted tone ring
• Worn wheel bearing affecting the signal
• Low brake fluid level
• ABS pump or control unit fault

How ABS diagnostics and repairs work

A proper diagnosis starts by reading the stored fault codes from the ABS control unit with the right equipment. Many generic code readers do not talk to the ABS module at all. The code usually points to a circuit or a wheel, for example a signal fault at the front left sensor, and from there tests confirm whether it is the sensor, the wiring, the ring or something else.

At Banks of the Tyne in Hebburn we carry out ABS diagnostics and repairs, so we can trace the cause instead of just clearing the light. Clearing the code without fixing the fault just means the light returns. What the repair costs depends on what is found.

MOT relevance

An ABS warning light that stays on can be a failure at the MOT, as the system is checked as part of the inspection. The exact rules and how defects are categorised are set by the DVSA, so check the current official guidance if you are close to a test date.

Whatever the MOT says, the practical point stands: the light is there because something is wrong. Having it looked at promptly is better than waiting for a test.

Frequently asked questions