A rotary actuator is provided for a motor vehicle, having a control knob, a housing, an actuating shaft that is rotationally fixed to the control knob, and electromagnetic means that act on the control knob so as to permit a detent or locking of the rotation of the control knob, wherein a coil is arranged in the housing in a rotationally fixed manner, and a disk-shaped flux guide is attached to the actuating shaft so as to be rotationally fixed and movable along the actuating shaft, and the flux guide can be pressed against the coil and/or the housing.