GM Caprice 1990-1993 Repair Guide

Description and Operation


The purpose of the Anti-Lock Brake System (ABS) is to minimize wheel lockup during heavy braking on most road surfaces. The ABS performs this function by monitoring the speed of each wheel and controlling the brake fluid pressure to each front wheel and both rear wheels during a braking maneuver. This allows you (as the driver) to retain directional stability and steering capability.

ABS continuously monitors all of its components and uses several methods of determining a fault and notifying the driver of a system malfunction. When the vehicle is started, a functional check of the ABS electrical circuitry is performed. As the vehicle speed reaches 4 mph, a functional check of the hydraulic modulator takes place. During this check each valve is cycled and the pump motor is turned on briefly. You may hear or feel this check take place when the vehicle begins to move. This test will only occur with each ignition startup and is considered normal operation. If a malfunction should occur the Brake warning lamp or the Anti-Lock warning lamp will either stay on or begin to blink.

Only a qualified technician should perform diagnostics and repairs, due to the complexity of this system. However some system components will have to be removed in order to obtain access to other parts.


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

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 hours. The system may be exposed to temperatures up to 200°F (95°C) for less than 15 minutes.
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 (for example: the modulator); 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.