Hydraulic Control Assembly - Antilock Brakes: Service and Repair

Hydraulic Control Unit

Special tools, testers and auxiliary items required

• Torque Wrench (V.A.G 1331)

• Brake Pedal Actuator (V.A.G 1869/2)

• Repair Kit Plugs (1H0 698 311 A)

Removing

Component location:

Hydraulic unit is located at left of engine compartment.





CAUTION!
Brake lines must not be bent.

- If the vehicle has a coded radio, get the radio code from the customer before beginning.

- Disconnect battery.

- Remove the rubber seal - 1 -.





- Remove plenum chamber cover.

- Remove coolant reservoir hex head screw -1-.





- Disconnect the connector on the coolant reservoir.

- Lay aside reservoir.

- Install the Brake Pedal Loading Device (V.A.G 1869/2) between the brake pedal and driver seat. Depress the brake pedal a minimum of 60 mm.





- Connect the bleeder bottle hose to the bleeder screws on the left front and left rear brake calipers. Open the bleeder screws.

• This lowers the pressure in the hydraulic unit.

- Close the left front and left rear bleeder screws.

- Do not remove Brake Pedal Loading Device (V.A.G 1869/2).

- To protect against escaping brake fluid, place a lint-free rag in the area under the control module and hydraulic unit.

• Number brake lines.

CAUTION!
Do not bend the brake lines near the hydraulic unit.

- Remove the brake lines and master brake cylinder.





- Remove remaining brake lines - arrows - from hydraulic unit.

- Seal the brake lines and threaded bores with sealing plugs from the repair set.

- Push the red circlip upward.





• Make sure that no brake fluid gets into the control module connector housing. This could lead to corrosion of the contacts and thereby cause the system to fail.

• Clean a dirty connector housing thoroughly with compressed air.

- Release connector at control module - arrow - and remove.

- Slide securing bracket in - direction of arrow - and remove connector.





- Remove bolts - 1 -.





- Remove hydraulic control unit.

Installing

Installation is the reverse of removal, with special attention to the following:

• Do not remove sealing plugs at new hydraulic unit until the corresponding brake line is about to be installed.

• If the sealing plugs are removed too early, brake fluid can escape and unit may not be sufficiently filled or adequately bled.

- Install the hydraulic unit into the bracket.

- Connect lines according to identification:





1 to the right front brake caliper"VR" (FR)
2 to the left rear brake caliper "HL" (LR)
3 to the right rear brake caliper "HR" (RR)
4 to the left front brake caliper "VL" (FL)
5 to the primary piston circuit "HZ 1"
6 to the secondary piston circuit "HZ 2"

• Do not tighten bolts completely. This makes it easier to fasten the individual brake lines to the hydraulic unit.

- Connect the connector to the hydraulics control module.

- Push the red circlip downward.





Tighten all the brake lines to the hydraulic unit and master brake cylinder.

- After tightening the brake lines, tighten the hydraulic unit - 1 -.





- Remove Brake Pedal Loading Device (V.A.G 1869/2).

- Bleed the brake system, refer to => [ Bleeding Brake System ] Procedures.

- Code ABS Control Module (J104). => Code The Control Module Using Vas 5051 In Guided Fault Finding.

- If control module is replaced, select "Replace" function for respective control module in "Guided Fault Finding".

Use the Vehicle Diagnosis, Testing And Information System (VAS 5051B) or (VAS 5052.).

- After fastening the brake lines to the hydraulic unit, perform the output check diagnosis. => Vehicle Diagnosis, Testing And Information System (VAS 5051B) or (VAS 5052)

• Using the output diagnostic test mode will tell if any line connections were interchanged.

Tightening Specifications