The base brake's hydraulic system must be bled anytime air enters the hydraulic system. The ABS though, particularly the ICU (HCU), should only need to be bled when the HCU is replaced or removed from the vehicle. The ABS must always be bled anytime it is suspected that the HCU has ingested air. Under most circumstances that require the bleeding of the brakes hydraulic system, only the base brake hydraulic system needs to be bled.
When bleeding the ABS system, the following bleeding sequence must be followed to insure complete and adequate bleeding.
WARNINGWhen bleeding the brake system, wear safety glasses. A clear bleed tube must be attached to the bleeder screws and submerged in a clear container filled part way with clean brake fluid. Direct the flow of the brake fluid away from yourself and the painted surfaces of the vehicle. Brake fluid at high pressure may come out of the bleeder screws when opened.
Make sure all hydraulic fluid lines are installed and properly torqued.
Bleed the base brake system using the standard pressure or manual bleeding procedure.