Brake Operating Unit (BOU) Expansion Reservoir: Removal

1. Remove key from ignition. Vehicles with Keyless Go, press start/stop button repeatedly until ignition is switched OFF.
2. Open engine hood.
3. Remove cover (1) from expansion reservoir (7). See Fig 1 .
NOTE: Even the smallest dirt particles in the hydraulic components can lead to brake system malfunctions.
4. Clean area around expansion reservoir thoroughly.
5. Remove plug (5) from brake fluid indicator switch (S11). The plug must be put down in a protected area so that it does not come into contact with brake fluid.
6. Unscrew cap (2) and take filter screen out of reservoir. Mark fill level of brake fluid on reservoir.
7. Suction off brake fluid from reservoir.
8. Remove hydraulic line (3a and 3b) from reservoir and seal immediately with stop plugs. Place hydraulic lines pointing upwards so that no brake fluid can run out and air cannot get into the hydraulic lines.
9. Unscrew bolt (6) of reservoir.
10. Pull reservoir out of BOU and remove. The openings in the BOU must constantly be filled up to the edge with brake fluid. Even the smallest dirt particles in the hydraulic components can lead to brake system malfunctions.

Fig 1: Removing & Installing Brake Operating Unit (BOU) Expansion Reservoir

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.