Audi Cars 1999-05

Hydraulic Control Unit (HCU)

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The hydraulic unit is located in the engine compartment. During operation of the anti-lock system, a pulsing may be felt at the brake pedal and a clicking heard from the hydraulic unit when the ABS system is activated.


WARNING
If the vehicle is equipped with the Electronic Stability Program (ESP), the ESP pump must be actuated during the bleeding procedure, using a proper scan tool, such as VAG 1551, VAG 1552, or equivalent, capable of activating the ESP pump.

Removal & Installation



  1. Disconnect the negative battery cable.
  2.  
  3. Using a clean, suitable baster or equivalent, withdraw the brake fluid from the reservoir.
  4.  
  5. Detach the central electrical connector.
  6.  
  7. Attach a bleeder hose installed into a suitable container to the left front brake caliper and open the bleeder screw.
  8.  
  9. Press the brake pedal down at least 2 1 / 3 inches (60mm) and using a suitable brake pedal depressor, such as VAG1813, hold the pedal in this position, then close the bleeder screw.
  10.  
  11. Cover the engine compartment to make sure any residual brake fluid does not damage the exposed areas.
  12.  
  13. Label, then disconnect the fluid lines.
  14.  
  15. Seal the lines and threaded holes in the hydraulic unit with suitable plugs, such as those included with repair kit Part No. 1H0 698 311 A.
  16.  
  17. Remove the mounting fasteners for the control unit and remove the control unit.
  18.  
  19. Installation is in reverse order of removal noting the following:
  20.  
  21. Do NOT remove the sealing plug for any of the fluid lines or ports until ready to attach the fluid lines. Remove only one line and port plug and attach one line at a time.
  22.  
  23. Bleed the brake system and check for adequate pedal pressure.
  24.  
  25. Connect the battery and enter the radio code.
  26.  

 
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