Abs Repair Instructions

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

Vehicles with ABS Mark 60 or ABS Mark 70 do not have a mechanical brake pressure regulator. A specially coordinated software program inside the ABS Control Module -J104- determines brake pressure allocation at the rear axle.

NOTE:

ABS malfunctions do not affect the brake system and the brake booster. Conventional brake system stays operative even without ABS. A change in braking behavior should be checked. When the ABS Warning Lamp -K47- is lit up, the rear wheels may lock prematurely during braking!

Fig 1: Identifying Brake Booster With Tandem Master Cylinder

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

ABS Hydraulic Unit -N55- with ABS Control Module -J104-.
Brake booster with tandem master cylinder.

The ABS Control Module -J104- -1- and the ABS Hydraulic Unit -N55- -2- are a single unit. Separation can only be performed when removed from vehicle. The pump -3- must not be separated from the ABS Hydraulic Unit -N55-.

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

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

Separation cannot be performed on vehicles with hydraulic brake booster or hill assist.

First determine the cause of the damage and then get the coding from the ABS Control Module -J104- using the Vehicle Diagnostic Tester before performing any service work on the anti-lock braking system.

Turn off the ignition and disconnect the battery ground cable.
Carry out before welding with an electric welding tool, refer to Body Repair Information.
When working with brake fluid, observe relevant safety precautions and notes, refer to GENERAL INFORMATION .
After finishing any work that required opening the brake system, bleed the brake system using the Brake Charger/Bleeder Unit VAS5234.
During final road test, carry out at least one ABS-controlled braking operation (appropriate pulsations must be felt at brake pedal).
It is necessary to maintain a high level of cleanliness when working on the ABS system.
Do not use any products containing mineral oil, such as oils, greases etc.
Thoroughly clean all unions and the adjacent areas before loosening. Do not use aggressive cleaning agents such as brake cleaner, fuel, thinners or similar chemicals.
Place parts that have been removed on a clean surface and cover.
Use the valve body transportation protection after disconnecting it from the ABS Control Module -J104- and the ABS Hydraulic Unit -N55-.
Carefully cover or seal any open components if the repairs cannot be performed immediately (use plugs1H0 698 311 A).
Only use lint-free cloths.
Only unpack replacement parts immediately prior to installation.
Only use parts in their original packaging.
When the system is open do not work with compressed air or do not move the vehicle.
The ABS Control Module -J104- may be briefly exposed to a maximum temperature of 95 °C when painting.
The ABS Control Module -J104- can be exposed to a maximum temperature of 85 °C only briefly.
Make sure that brake fluid does not enter harness connectors.