See Figure 1
The Anti-lock Braking System (ABS) is standard equipment on all J-body cars covered by this guide. ABS provides the driver with 3 important benefits over standard braking systems: increased vehicle stability, improved vehicle steerability, and potentially reduced stopping distances during braking. It should be noted that although the ABS-VI system offers definite advantages, the system cannot increase brake pressure above master cylinder pressure applied by the driver and cannot apply the brakes itself.
The ABS-VI Anti-lock Braking System consists of a conventional braking system with vacuum power booster, compact master cylinder, front disc brakes, rear drum brakes and interconnecting hydraulic brake lines augmented with the ABS components. The ABS-VI system includes a hydraulic modulator assembly, Electronic Brake Control Module (EBCM) or Electronic Brake and Traction Control Module (EBTCM) (these are all different Computer Control Modules which differ depending upon vehicle year and application), a brake fluid level sensor, a system relay, 4 wheel speed sensors, interconnecting wiring and an amber ABS warning light.
The EBCM/EBTCM monitors inputs from the individual wheel speed sensors and determines when a wheel or wheels is/are about to lock up. The EBCM/EBTCM controls the motors on the hydraulic modulator assembly to reduce brake pressure to the wheel about to lock up. When the wheel regains traction, the brake pressure is increased until the wheel again approaches lock-up. The cycle repeats until either the vehicle comes to a stop, the brake pedal is released, or no wheels are about to lock up. The EBCM/EBTCM also has the ability to monitor itself and can store diagnostic codes in a non-volatile (will not be erased if the battery is disconnected) memory. The EBCM/EBTCM is serviced as an assembly.
The ABS-VI braking system employs 2 modes: base (conventional) braking and anti-lock braking. Under normal braking, the conventional part of the system stops the vehicle. When in the ABS mode, the Electromagnetic Brakes (EMB) action of the ABS system controls the two front wheels individually and the rear wheels together. If the one rear wheel is about to lock up, the hydraulic pressure to both wheels is reduced, controlling both wheels together.