General 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 inside the ABS Control Module -J104- determines the brake pressure allocation for the rear axle.

NOTE:

ABS malfunctions do not affect the brake system and the booster. The conventional brake system remains operative even without ABS. A change in braking behavior must be anticipated. When the ABS indicator lamp comes on, the rear wheels may lock prematurely when braking!

LHD Layout:

Fig 1: Configuration

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

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

2 - Brake Booster

The ABS Hydraulic Unit -N55- and ABS Control Module -J104- are one unit. Separation is only possible when removed. The hydraulic pump may also not be separated from the ABS Hydraulic Unit -N55-.

Anti-Lock Braking System (ABS) Repair Information

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. Refer to 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 in the appropriate Service Information.
When handling brake fluid, observe the relevant safety precautions and notes.
After finishing any work that required opening the brake system, bleed the brake system using the Brake Charger/Bleeder Unit: VAS5234 .
During the final road test, make sure a controlled braking maneuver is performed at least once (pulsing must be felt on the brake pedal).
It is necessary to maintain a high level of cleanliness when working on the ABS system.
Do not use fluid containing mineral oils, for example, oils, grease, 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. (Use plugs from repair set 1 H0 698 311 A)
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 in the ABS Control Module -J104- cannot be readjusted.
The valve coils in the ABS Control Module -J104- 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 can be taken at the contacts inside the ABS Control Module -J104-.
No measurements can be taken at the contacts inside the ABS Hydraulic Unit -N55-.
The valve bodies inside the ABS Hydraulic Unit -N55- must not be damaged or bent.
The contacts cannot be replaced.
Using contact sprays on the contacts and pressure sensor are not permitted.
No foreign objects may be between the ABS Control Module -J104- and the ABS Hydraulic Unit -N55-.
During paint work, the ABS Control Module -J104- may be briefly exposed to a maximum temperature of 95 °C (203 °F).
The ABS Control Module -J104- may be exposed to a temperature of 85 °C (185 °F) for approximately two hours.
Make sure that brake fluid cannot get into the connectors.