Anti-Lock Braking System (Abs) Repair Information

The ABS brake system is divided diagonally. The brake booster operates pneumatically via the vacuum brake booster.

Vehicles 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 layout, LHD:

Fig 1: ABS Layout, LHD:

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

1 -  ABS Hydraulic Unit -N55- and ABS Control Module -J104-

2 -  Brake Booster

The control module and hydraulic unit form one component. Separation is only possible when removed. The hydraulic pump must also not be separated from the hydraulic unit.

• Before servicing the ABS, determine the cause of damage as well as the control module code using "Guided Fault Finding".

"Guided Fault Finding" is performed using a Vehicle Diagnostic Tester.

• Disconnect the battery ground cable when the ignition is switched off.
• Before welding with an electric welding tool, observe the information found here: refer to the appropriate Service Information.
• When handling brake fluid, observe the relevant safety precautions and notes. Refer to BRAKE FLUID GENERAL INFORMATION .
• After finishing any work that required opening the brake system, bleed the brake system using the Brake Filling and Bleeding Equipment:VAS 6860US  . Refer to HYDRAULIC SYSTEM, STANDARD BLEEDING .
• During the final road test, make sure a controlled braking maneuver is performed at least once. A pulsation must be felt at the brake pedal.
• It is necessary to maintain a high level of cleanliness when working on the ABS system.
• It is not permitted to use any products which contain mineral oil, such as oils, greases etc.
• Thoroughly clean all connection points and their surrounding areas before loosening. However, do not use aggressive cleaning agents such as brake cleaner, gasoline, thinners or similar compounds.
• Place the removed parts on a clean surface and cover them.
• Carefully cover or seal opened components if the repair is not performed immediately.
• Only use lint-free cloths
• Remove the replacement parts from their packaging just prior to installing them.
• Only use parts in their original packaging.
• Do not work with compressed air when the system is open. Do not move the vehicle.
• The valve coils inside the control module cannot be readjusted.
• The valve coils inside the control module cannot be replaced.
• The pressure sensor must not be changed or damaged.
• The pressure sensor cannot be replaced.
• The sensor housing must not be under any mechanical load.
• No measurements may be performed on the contacts in the control module.
• No measurements may be performed on the contacts in the hydraulic unit.
• The valve bodies inside the hydraulic unit must not be damaged or bent.
• The contacts cannot be replaced.
• Using contact sprays on the contacts and pressure sensor are not permitted.
• Make sure there are no foreign objects between the control module and the hydraulic unit.
• The electronic control module can be exposed to a maximum temperature of 95 °C (203 °F) only briefly, and to a maximum of 85 °C (185 °F) for longer periods (approximately two hours). Make sure that brake fluid cannot get into the connectors.