Anti-Lock Brake System - 4-Wheel: Description

NOTE: All 2WD Astro and Safari vehicles use 3 wheel speed sensors. All-Wheel Drive (AWD) Astro and Safari vehicles use 4 wheel speed sensors.

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 Brake Pressure Modulator Valve (BPMV), Vehicle Speed Sensor (VSS) buffer, Vehicle Speed Sensor (VSS), wheel sensors, warning lights, electrical wiring and hydraulic lines.

The BPMV consists of an Electronic Control Unit (ECU), hydraulic control unit, 2 accumulators, pump motor and a relay. See Fig 1 -4. The hydraulic control unit consists of an isolation solenoid valve, Pulse-Width Modulated (PWM) 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 BPMV is necessary, replace complete assembly.

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.

Fig 4: 4WAL Brake System Component Location ("G" Series)

Courtesy of GENERAL MOTORS CORP.