Anti-Lock Brake System - 4-Wheel: Description

The Kelsey-Hayes 4-Wheel Anti-Lock (4WAL) brake system is used to prevent wheel lock-up during heavy braking. This allows driver to maintain steering control while stopping vehicle in shortest distance possible. The system consists of Electro-Hydraulic Control Unit (EHCU), 4 wheel sensors, warning lights, electrical wiring and hydraulic lines.

The EHCU consists of an Electronic Control Unit (ECU), hydraulic control unit, 2 accumulators, pump motor and a relay. See Fig 1, Fig 2 or Fig 3. The hydraulic control unit consists of an Isolation Solenoid Valve (ISO), Pulse-Width Modulated (PVM) valve, a High Pressure Accumulator (HPA), Low Pressure Accumulator (LPA) and a reset switch on each channel. If overhaul or repair to any component on the EHCU is necessary, complete assembly must be replaced.

Fig 1: 4WAL Brake System Component Locations (Astro & Safari)

Courtesy of GENERAL MOTORS CORP.

Fig 2: 4WAL Brake Sys Series Component Locations (Bravada, "S" & "T"

Courtesy of GENERAL MOTORS CORP.

Fig 3: 4WAL Brake System Component Locations ("C" & "K" Series)

Courtesy of GENERAL MOTORS CORP.