Anti-Lock Brake System: Description

NOTE: General Motors uses several different anti-lock brake systems. Ensure appropriate ANTI-LOCK article is being used.

NOTE: See ANTI-LOCK BRAKE SAFETY PRECAUTIONS article in GENERAL INFORMATION before servicing any anti-lock brake system.

NOTE: All models are equipped with an Electronic Brake Control Module (EBCM).

NOTE: For more information on brake system, see BRAKE SYSTEM article.

The ABS-VI system uses electric motors to modulate displacement pistons. The ABS hydraulic modulator assembly is mounted on master cylinder/vacuum booster assembly. See Fig 1 . The modulator contains 3 electric motors, which control pistons for brakeline pressure regulation. Major components of ABS-VI system include hydraulic modulator, 4 wheel speed sensors, system enable relay, 2 or 3 dash-mounted warning lights and Electronic Brake Control Module (EBCM).

Each motor drive gear operates a threaded shaft assembly attached to a pressure modulating piston. The motor drives piston up and down to increase and decrease brake line pressure, respectively. When EBCM senses wheel lock-up from the wheel speed sensors, a solenoid, located in the hydraulic modulator, closes the hydraulic path from the master cylinder. The electric motor for that brake circuit then cycles the piston up and down to modulate braking force, preventing wheel lock-up.

Fig 1: Locating Anti-Lock Brake System Components (Typical)

Courtesy of GENERAL MOTORS CORP.