GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

Description and Operation


Anti-lock brakes provide the driver with 3 important benefits over standard braking systems: increased vehicle stability, improved vehicle steerability and potentially reduced stopping distances during braking.

The ABS-VI Anti-lock Braking System consists of a conventional braking system with a 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 components consist of a hydraulic modulator assembly, Electronic Control Unit (ECU), a system relay, 4 wheel speed sensors, interconnecting wiring and an amber ABS warning light.

The ECU monitors inputs from the individual wheel speed sensors, then determines when a wheel or wheels are about to lock-up. The ECU 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 ECU 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 ECU is serviced as an assembly.

The ABS-VI braking system employs 2 modes, the base (conventional) braking and the anti-lock braking. Under normal braking, the conventional part of the system stops the vehicle. When in the ABS mode, the system controls the 2 front wheels individually and the rear wheels together. If a rear wheel is about to lock-up, the hydraulic pressure to both wheels is reduced, controlling both wheels together. Since the vast majority of the braking is controlled by the front wheels, there is no adverse effect on vehicle control during hard braking.


Failure to observe the following precautions may result in system damage.

Performing diagnostic work on the ABS-VI requires the use of a Tech I Scan diagnostic tool or equivalent. If unavailable, please refer diagnostic work to a qualified technician.
Before performing electric arc welding on the vehicle, disconnect the Electronic Brake Control Module (EBCM) and the hydraulic modulator connectors.
When performing painting work on the vehicle, do not expose the Electronic Brake Control Module (EBCM) to temperatures in excess of 185°F (85°C) for longer than 2 hrs. The system may be exposed to temperatures up to 200°F (95°C) for less than 15 min.
Never disconnect or connect the Electronic Brake Control Module (EBCM) or hydraulic modulator connectors with the ignition switch ON.
Never disassemble any component of the Anti-Lock Brake System (ABS) which is designated non-serviceable; the component must be replaced as an assembly.
When filling the master cylinder, always use Delco Supreme 11 brake fluid or equivalent, which meets DOT 3 specifications; petroleum base fluid will destroy the rubber parts.