Removal and installation of the electronic control unit with the hydraulic unit (VW Passat B4)

The unit is installed in the engine compartment on the left. The electronic unit is attached to the hydraulic unit with bolts.

Warning: When removing the unit, do not twist the pipes connected to the hydraulic unit.

To remove, disconnect the wires from the battery terminals. Remove the expansion tank of the engine cooling system and move it to the side. Disconnect the ECU connector by unfastening its latch.

Attach the brake bleed hose to the left front brake bleed nipple, place the other end of the hose in a container with clean brake fluid and loosen the bleed nipple. Press the brake pedal to 60 mm of its travel and, holding it in this position, tighten the left front brake bleed nipple.

Remove the protective casing covering the master brake cylinder and hydraulic unit. Disconnect the brake pipes from the hydraulic unit and plug the openings in the pipes and hydraulic unit. Loosen the T25 socket head cap screws securing the hydraulic unit to the bracket. Disconnect the hydraulic pump electric motor connector from the ECU. Loosen the ECU mounting bolts to the hydraulic unit and disconnect it. When removing the ECU, ensure that it is not skewed. Cover the ECU magnetic coils with a clean, lint-free cloth.

Note: When installing a new hydraulic unit, remove the plugs that close its threaded holes only immediately before connecting the corresponding pipeline. If the plugs are removed prematurely, fluid may leak out of the hydraulic unit, which may result in it not being completely filled with fluid and not being completely removed from the air.

The original can be found at (VWmanual)

Before installation, clean the location of the ECU unit with the hydraulic unit. Install the ECU on the electromagnetic valves of the hydraulic unit before seating the ECU housing on the hydraulic unit housing. Tighten new bolts fastening the ECU to the hydraulic unit and tighten them to a torque of 0.4 kgf·m. Connect the hydraulic pump electric motor connector to the ECU.

Perform the remaining installation operations in the reverse order of removal.

Bleed the brake hydraulic system as described above. Enter the code into the electronic control unit.