Hydraulic Control Assembly - Antilock Brakes: Description and Operation

The Hydraulic Control Unit (HCU) consists of a valve block assembly, pump/motor assembly, and a fluid reservoir with a fluid level switch. The HCU is located on the left frame rail forward of the master cylinder.

There are two Hydraulic Control Units. One for ABS only, and one for ABS and traction control combined. If a new HCU unit is installed with the wrong type of Controller, Antilock Brake (CAB), the system will disable itself and a diagnostic trouble code will be stored.