ABS and Vehicle Stability Systems
Anti-lock brakes, stability control and the systems built on them are why a modern car can brake hard and swerve without spinning out. Here’s what each one does, how to tell it’s working, and what to check before you buy a used car.
The systems, in plain English
Anti-lock brakes (ABS)
Standard todaySensors watch each wheel. If one is about to lock under hard braking, ABS releases and reapplies that brake many times a second, so the tyre keeps its grip and you can still steer around trouble. You’ll feel the pedal pulse: keep pressing firmly.Brake-force distribution (EBD)
Shares braking effort between the front and rear wheels, and side to side, to suit the load and the grip available. It works alongside ABS, and you won’t notice it doing so.Brake assist
Recognises an emergency stop from how fast you hit the pedal and adds full braking force, because most drivers don’t press hard enough in a panic.Stability control (ESC)
Look for itCompares where you’re steering with where the car is actually going. If it starts to skid, ESC brakes individual wheels and can ease the power to bring it back into line. Makers also call it VSC, VDC, DSC or ESP.Traction control
Stops the driven wheels spinning when you accelerate on wet, gravel or icy roads, by braking the spinning wheel or easing the power.Autonomous emergency braking (AEB)
Newer vehiclesWatches the road ahead with a camera, radar or both. If you don’t react to a vehicle in your path, and on many systems a pedestrian or cyclist, it warns you and then brakes on its own.Regenerative braking
Electric and hybrid vehicles slow partly by using the motor as a generator, topping up the battery. The car blends this with its normal brakes, so the pedal feels much the same, but discs that rarely do much work can corrode.Torque vectoring
Sends more drive, or a touch of braking, to particular wheels in a corner to help the car turn in. Common on all-wheel-drive and performance cars.
What the warning lights mean
Dashboard lights for the braking and stability systems
| You see | What it means |
|---|---|
| All the lights on for a moment at start-up | Normal. The car is testing its systems, and the lights should go out within a few seconds. |
| ABS light stays on | ABS has a fault and won't work. The ordinary brakes still do, but get it checked before relying on the car. |
| Stability or traction light flashing | The system is working right now because the road is slippery. Ease off. |
| Stability or traction light on steadily | The system has been switched off, or has a fault. |
| Red brake warning light | The handbrake may be on, the brake fluid may be low, or there's a fault. Stop and get it checked. |
Buying a used car: what to check
- Watch the dashboard at start-up. The ABS, stability and airbag lights should come on briefly and then go out. A light that never comes on at all can mean a fault is being hidden.
- Brake firmly on the test drive, somewhere safe and empty. The car should stop straight, without pulling, juddering or grinding.
- Ask about the windscreen. If it has been replaced on a car with AEB or lane-keeping cameras behind the glass, the camera needs recalibrating. Ask for proof it was done.
- On an EV or hybrid, ask when the brakes were last serviced: discs that rarely do much work can rust.
- Check the tyres. These systems can only use the grip the tyres have. The legal minimum tread depth in New Zealand is 1.5 mm, and more is safer in the wet.
- Get a mechanical inspection of the brakes and suspension before you buy, as our car buyer’s guide explains.
A short history
Anti-lock braking began on aircraft, where locking a wheel on landing could burst a tyre. Early mechanical systems reached a handful of cars in the 1960s, and the first fully electronic four-wheel ABS arrived on the Mercedes-Benz S-Class in 1978. Stability control followed in the mid-1990s, built on the same wheel-speed sensors, and the camera and radar systems of today build on both.
Does the car you're looking at have ABS and traction control?
A vehicle report lists the safety features recorded for its model, such as airbags, ABS and traction control, and its driver safety rating where one has been published, alongside money owing, odometer and stolen checks.