Anti-Lock Brake System - Four Wheel

The Kelsey-Hayes 4 Wheel Anti-Lock (4WAL) brake system is optional on Astro, and Safari 2WD and 4WD models. This system is used to prevent wheel lock-up during heavy braking. This allows driver to maintain steering control while stopping the vehicle in the shortest distance. The system consists of: Electro-Hydraulic Control Unit (EHCU), 4 wheel sensors, warning lights, electrical wiring and hydraulic lines.

The EHCU is located on firewall, under the master cylinder. It consists of an Electronic Control Unit (ECU), hydraulic control unit, 2 accumulators, pump motor and a relay. 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 of each channel. If overhaul or repair to any component on the EHCU is necessary, complete assembly must be replaced.

Components unique to the anti-lock brake system are covered in a separate article. See ANTI-LOCK BRAKE SYSTEM article in the BRAKES Section.