Antilock Brake System

The ABS brake system is divided diagonally (two circuits). The vacuum brake servo unit boosts the brakes pneumatically.

Models with ABS do not have a mechanical brake pressure regulator. A specially coordinated software program in the control module determines brake pressure allocation at the rear axle.

ABS disturbances do not affect the brake system and the booster. Conventional brake system stays operative even without ABS. A change in braking behavior should be checked. When the ABS warning lamp lights up, the rear wheels may lock prematurely during braking.

ABS Allocation 

Fig 1: Identifying Hydraulic Unit And Control Module And Brake Booster

Courtesy of VOLKSWAGEN UNITED STATES, INC.

1 - Hydraulic unit and control module

2 - Brake Booster

Control module -1- and hydraulic unit -2- comprise a single unit. Separation can only be performed when removed from vehicle. The hydraulic pump -3- must not be separated from the hydraulic unit.

Fig 2: Identifying Control Module, Hydraulic Unit And Hydraulic Pump

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Separation is not possible on vehicles with ABS/EDL/ASR/ESP with hydraulic brake booster or hill assist.