Servotronic Valve
WARNING: This page does not describe the selected car, but rather 15 other vehicles, including the 2006 BMW 530i, 2006 BMW 525i, 2006 BMW 330xi, 2006 BMW 330i, and 2006 BMW 330Ci. However, it is still accessible from the selected car via links, so may be relevant.
If a fault occurs (when de-energized, for example) the Servotronic valve switches to the characteristic for high speeds. Steering assistance is reduced accordingly.