| Vian kuvaus | The fault relates to the welding of the hollow shaft of the servomotor. Brake pressure is built up and brake force assistance are provided by an integrated electric servomotor. The hollow shaft of the servomotor was not welded according to specification, resulting in a lack of connection (gap) between bearing bush and hollow shaft. Therefore, the bearing bush is not properly fixed. During the subsupplier's production process, an incorrect calibration of the welding system was carried out, resulting in a permanent offset of 0.2 mm of the position axis for laser welding. In addition, a random presence of welding spatter during the reference measurement can result in an incorrect position of the hollow shaft being measured and the bearing bush being positioned accordingly incorrectly. If this welding spatter is >0.05mm and with a deviation explained above at the same time, this would be out of tolerance. In very rare cases, the weld cannot withstand and breaks if a high brake pressure is suddenly built up. If this occurs, the system switches into emergency mode. In emergency mode, the hydraulic pressure on the front axle is built up through foot respectively pedal force only. The rear axle brake circuit fails. The braking effect on the rear axle is built up and regulated electromechanically by electric parking brake actuators. Therefore, it is necessary to brake more forcefully, which extends the braking distance. Support from antilock braking systems (ABS) and dynamic stability control (DSC) is not provided. On September 11, 2024, BMW decided to initiate the safety recall “Servomotor Brake Booster (Hydraulic)” regarding BMW models F9x G0x G18 G6x G70 U06 U1x and MINI models F66, J0x and U25. On affected vehicles the brake system will be replaced. |
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