Antilock Brakes / Traction Control Systems: Description and Operation

Fig. 1 Anti-lock Brake System Overview:

Refer to Fig. 1, for overview of anti-lock brake system.
The purpose of the anti-lock brake system is to prevent wheel lock-up under heavy braking condition, on virtually any road surface. When a wheel locking condition exists, the pressure modulator valve (PMV) assembly isolates each individual wheel hydraulic circuit, then begins modulation of fluid pressure to each wheel according to wheel speed input to the EBCM. The PMV is controlled by the Electronic Brake Control Module (EBCM).
Modulation occurs by means of three ABS modes: pressure hold, pressure reduce and pressure increase. The PMV assembly has two valves per individual hydraulic circuit. These valves work in pairs to achieve the three ABS modes. The ABS system isolates, monitors and controls and wheels simultaneously.