Under what circumstances does ABS activate?

[NorahFitz]

ABS activates during emergency braking, and it will also trigger when braking hard on slippery or icy roads. ABS stands for Anti-lock Braking System. During emergency braking, the ABS system allows the wheels to maintain a rolling-while-sliding state. It prevents wheel lock-up during hard braking, as locked wheels can cause skidding and loss of control. If all wheels lock up, the driver cannot steer the vehicle using the steering wheel. Typically, a driver's instinctive reaction in an emergency is to stomp the brake pedal fully. Without ABS, the vehicle would quickly lose control. The ABS system exists to prevent this situation - it maintains the wheels in a rolling-while-sliding state during emergency braking, essentially performing pulsed braking on the wheels. ABS can apply brakes 60 to 120 times per second to each wheel.