GM Full-Size Trucks 1988-1998 Repair Information

General Information


The Kelsey Hayes four wheel anti-lock brake system is used on the 1992-98 Suburban, Jimmy, Yukon and Blazer and C/K Series trucks.

The 4 wheel anti-lock system is designed to reduce brake lock-up during severe brake application. The Electro-Hydraulic Control Unit (EHCU) valve-located near the master cylinder-controls the hydraulic pressure within the brake lines.

The control valve is made up of 2 types of valves. Each front wheel and the combined rear wheel circuit are served by a dedicated isolation valve and a dump valve. The isolation valves maintain pressure within their respective circuits; the dump valves release pressure within each circuit as commanded by the EHCU. The valves are controlled by a micro-computer within the EHCU valve.

In a severe brake application, the EHCU valve will either allow pressure to increase within the system or maintain (isolate) the pressure within the system or release existing pressure through the dump valves into the accumulators.

The EHCU valve operates by receiving signals from the speed sensors, located at each wheel, and from the brake lamp switch. The speed sensors connect directly to the EHCU valve through a multi-pin connector.

The system is connected to the ANTI-LOCK warning lamp on the dashboard. The warning lamp will illuminate for about 2 seconds every time the vehicle is started. The warning lamp will illuminate it the computer detects a problem within the anti-lock system during vehicle operation.