BMW Cars 1999-06

Hydraulic Control Unit (HCU)


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.

If the vehicle is equipped with ASC+T, the BMW Service Tester must be used to properly bleed the system. Due to safety and liability issues, this job should only be performed by a BMW dealer.

Removal & Installation

  1. Disconnect the negative battery cable.
  3. On M50 and M52 6 cylinder engines, remove the Mass Air Flow (MAF) sensor and if equipped with cruise control, unscrew the drive motor.
  5. Using a clean, suitable baster or equivalent, withdraw the brake fluid from the reservoir.
  7. Detach the central electrical connector.
  9. Disconnect and remove the fluid line from the front of the master cylinder to the front of the hydraulic unit.
  11. Label, then disconnect the remaining fluid lines.
  13. Remove the suction hoses off the elbows on the pump body taking care to catch the residual brake fluid.
  15. On models equipped with cruise control, unscrew the carbon filter for the EVAP system.
  17. Remove the mounting fasteners and then the hydraulic unit.

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Fig. The intake manifold has been lifted away to allow a more complete view of the ABS hydraulic unit-E36 model shown

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Fig. The unit on E36 models is between the rear of the left strut tower and the intake manifold, just below the master cylinder

To install:

  1. Installation is in reverse order of removal noting the following.
  3. The brake hoses must be connected in the proper location.
  5. The brake hydraulic system must be bled using fresh approved brake fluid.