I assume they mean the CAB (controller, anti-lock Brake) needs replacing and not the HCU (hydraulic control unit).
CONTROLLER ANTILOCK BRAKE
- Remove and isolate negative battery cable.
- Release CAB connector locking handle and remove connector CAB Harness Connector
- Remove the 2 CAB mounting bolts and remove CAB from bracket.
- Install CAB in mounting bracket.
- Install mounting bolts.
- Connect harness and lock into place with locking handle.
- Install negative battery cable.