Abs Repair Instructions

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

Left-Hand Drive Configuration 

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 can only be performed when removed from vehicle. The hydraulic pump may also not be separated from the ABS Hydraulic Unit -N55-.

Anti-Lock Braking System (ABS) Repair Information

• Before carrying out repair work on 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 one time (pulsing must be felt in 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-.
• The ABS Control Module -J104- may be briefly exposed to a maximum temperature of 95 °C (203 °F) when painting.
• 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.