An ABS light on your dashboard means the anti-lock braking system has found a fault and switched itself off. Your normal brakes usually still work, so you can generally drive carefully to a workshop, but the wheels can now lock under hard braking, and on most cars the traction control and stability control are switched off as well.
One of the most common causes is a faulty wheel speed sensor or its wiring, but low brake fluid and module faults can trigger it too. Here is what the systems do, what usually goes wrong, and how the light affects your WOF.
What ABS and traction control actually do
ABS (anti-lock braking system) stops your wheels locking up when you brake hard. Sensors at each wheel tell the ABS module how fast each wheel is turning. If one starts to slow much faster than the others, a sign it is about to lock and skid, the system rapidly pulses the brake pressure to that wheel so it keeps turning. That keeps you able to steer while braking hard, which matters on a wet road or loose gravel.
Traction control works the other way round. If a wheel spins faster than the others when you accelerate, it brakes that wheel or cuts engine power until it grips again.
Electronic stability control (ESC) builds on both. It compares where you are steering with where the car is actually going, and brakes individual wheels to help stop a skid.
All three share the same wheel speed sensors and, on most cars, the same control module. That is why one fault can light up several warnings at once.
What the warning lights mean
- Amber ABS light: the ABS has found a fault and is switched off. Normal braking is usually still there.
- Traction control or stability control light, flashing: the system is working right now, for example on a slippery road. That is normal.
- Traction control or stability control light, on steadily: the system has a fault or has been switched off.
- Red brake warning light: this is the serious one. It can mean low brake fluid, a problem with the brake system itself, or the park brake still being on. If it stays on with the park brake off, stop and get the car checked before driving further.
Common causes of an ABS light
Wheel speed sensors. These sit at each wheel, right in the firing line of water, mud, road grime and brake dust. A sensor can fail, get coated in metal dust, or have its wiring damaged. This is one of the most common causes of an ABS light.
Damaged wiring or connectors. The sensor wires run along the suspension and flex every time the wheel moves. They can chafe, corrode or get pulled during other work.
The tone ring. Each sensor reads a toothed or magnetic ring that turns with the wheel. If the ring is cracked, corroded or clogged, the sensor gets a bad signal. On many cars the ring is part of the wheel bearing or CV joint, so a worn wheel bearing can bring on an ABS light.
Low brake fluid. On some cars, a low fluid level can trigger the ABS or brake warning. Low fluid is also a sign that the pads are well worn or that there is a leak, so it is worth checking rather than just topping up.
The ABS module or pump. The module and hydraulic pump can develop faults, though this is less common than a sensor or wiring problem.
Battery and charging problems. The ABS module needs a steady voltage. A weak battery or a charging fault can throw up ABS and other warning lights that clear once the electrical problem is fixed.
Is it safe to drive with the ABS light on?
For most drivers, a steady amber ABS light on its own means you can drive carefully to get it checked. Your brakes will still stop the car. What changes is that the wheels can lock under hard braking, so in an emergency stop on a wet road you may skid and lose steering.
Until it is fixed:
- Leave a bigger gap to the car in front
- Brake earlier and more gently, especially on wet roads and gravel
- Take extra care with a load or a trailer on
- Get it checked soon, rather than living with it
Stop driving and get help if the red brake warning light is on as well, if the brake pedal feels soft, sinks or feels different, or if the car pulls to one side when braking. If you are hearing new noises when you brake, our guide to squeaky or grinding brakes explains what each one usually means.
Does an ABS light fail a WOF?
It can. NZTA’s Vehicle Inspection Requirements Manual lists these as reasons for rejection on a light vehicle:
- An ABS or brake system warning lamp or self-check system, where fitted, that indicates a defect in the ABS or brake system. This includes an ABS light that does not come on when the ignition is switched on, or one that does not go off after the car has been driven.
- An ABS system component that is damaged, insecure or missing.
- On a vehicle fitted with electronic stability control, a warning light that indicates an ESC fault, or an ESC system that has been removed.
You can read the full requirements on the NZTA Vehicle Inspection Portal. Rules are updated from time to time, so it is worth checking the current version with NZTA. Our guide to what fails a WOF in NZ covers the other common fail items.
How we diagnose an ABS light
Guessing at ABS faults gets expensive, because a sensor fault, a wiring fault and a tone ring fault can all set similar codes. At our Frankton workshop, we:
- Read the ABS module with manufacturer-level scan tools rather than a basic engine code reader, which often cannot see ABS faults at all
- Watch live wheel speed data from all four wheels, which usually shows exactly which sensor is dropping out
- Inspect the sensor, wiring, connectors and tone ring at the suspect wheel
- Check the brake fluid level and condition, and the pads and rotors, as part of a proper brake inspection
- Test the battery and charging system if several warning lights are on at once
Once we know the cause, we explain what we found and give you a free quote before any work goes ahead. If the light came on alongside other dashboard warnings, our guide to the check engine light is also worth a read.
Get your ABS light checked
An ABS light is the car telling you one of its safety systems is off. It is rarely an emergency on its own, but it is worth sorting before it turns into a WOF fail or catches you out on a wet road.
Call us on (07) 847 3339 or use the contact form to book an ABS and brake check at 281 Kahikatea Drive, Frankton, Hamilton. We work on petrol and diesel cars, utes, 4WDs and light commercials.