ABS warning light on: what does it mean and can I drive?
If the ABS light stays on, the anti-lock function has been switched off by a fault, though normal braking usually still works.
The ABS warning light means the car has detected a fault in its anti-lock braking system. In most cases the ordinary brakes still work, but the anti-lock function, which stops the wheels locking in a hard stop, may not be available. That reduces your safety margin, especially on wet or slippery roads.
The light should come on briefly when you switch on the ignition and then go out. If it stays lit, flashes or comes on while driving, there is a stored fault. Read on for the typical causes, what is safe to check and when to stop.
What does ABS actually do?
Anti-lock braking uses a sensor at each wheel to monitor its speed. If a wheel starts to lock under hard braking, a control unit and pump rapidly release and reapply pressure so you can keep steering. You may feel a pulsing in the pedal when it operates, and that is normal.
Many cars link other systems, such as traction control and stability control, to the same sensors. A fault can therefore bring up more than one warning light.
Why is my ABS light on?
The most common cause is a wheel speed sensor that has failed, become dirty or lost its signal. The wiring to the sensor can also be damaged by corrosion or road debris, and the toothed ring it reads can rust or crack. Less often the fault is in the ABS pump or control module.
Other causes include low brake fluid, a problem with the battery or charging system that affects voltage, or recent work on a wheel or hub where a connector was not refitted correctly. The cause cannot be known from the light alone.
- Wheel speed sensor fault or contamination
- Damaged or corroded wiring and connectors
- Rusted or damaged sensor ring
- Low brake fluid level
- Fault in the ABS pump or control unit
Is it safe to drive with the ABS light on?
If only the ABS light is on and the brake pedal feels normal, the car will usually still brake, but without anti-lock assistance. Drive gently, leave bigger gaps and arrange a check soon. Do not ignore it for weeks.
If the red brake warning light is on as well, or the pedal feels soft or low, stop driving. That combination can mean a hydraulic fault or low fluid, and the car should not be used until it has been checked. Your handbook will explain what each colour of warning light means.
How does a garage diagnose an ABS fault?
A diagnostic tool reads the fault codes stored in the ABS control unit, which usually points to the wheel or circuit affected. A code is a starting point rather than the answer. The garage then inspects the sensor, wiring, connector and ring, and checks the fluid level and the live readings from each wheel.
Cost depends on the finding. Cleaning or replacing a sensor is a smaller job than repairing wiring, and replacing a pump or control unit is larger. The make and model also matter. At Automaster, a garage at Longcombe Cross near Totnes, we find the cause first and then talk through the options.
Will an ABS warning light fail an MOT?
Yes, in most cases. A warning light that stays on for the ABS system is a reason for failure in the MOT test, because the system is a safety feature fitted by the manufacturer. A light that does not come on at start-up, which could mean the bulb is disabled, can also be flagged.
If your MOT is due, it is wise to have the fault looked at beforehand so that the test is not delayed.
A lit ABS light is a fault to diagnose, not a nuisance to ignore. Ask Automaster for a quote or call our quote line and we will read the codes and inspect the system.
Common questions
Can I reset the ABS light myself?
Clearing a code may turn the light off for a while, but if the fault remains it will return. It is more useful to find and fix the cause than to wipe the code.
Why did the ABS light come on in cold or wet weather?
Moisture can affect a corroded connector or a sensor and cause an intermittent fault. The light may go out again, but the stored fault still needs investigating.
Does the ABS light mean my brakes have failed?
Not usually. The ordinary hydraulic brakes normally still work, but the anti-lock function is reduced. If the red brake light is also on or the pedal feels odd, stop driving.
What should I tell the garage?
Tell us when the light came on, whether other lights appeared, whether the pedal feels different and whether any work had recently been done on the wheels or brakes.
More advice
Ask for a quote
Tell us the make, model, registration and what the car is doing, and we will come back to you. Prefer to talk? Call our quote line on 01803 862152.
Automaster, Longcombe Cross, Longcombe, Totnes TQ9 6PL, United Kingdom