Antilock Brakes / Traction Control Systems: Description and Operation

Fig. 5 Anti-lock Brake System:

The anti-lock brake system (ABS), Fig. 5 modulates the pressure of
the brake fluid applied to each caliper. This prevents the wheels from locking, whenever they are likely to be locked due to excessive braking. It then restores normal hydraulic pressure when there is no longer any possibility of wheel locking. The system has a fail safe function that allows normal braking if there is a problem within the system.