1. A method of detecting external impacts in vehicle steering systems which include a rotatable steering shaft and a servomotor for generating a steering assist torque, the method comprising the steps of: (a) continuously measuring a first characteristic; (b) continuously measuring a second characteristic; (c) forming tuples of characteristics at least from a measured value of the first characteristic and a simultaneously picked up measured value of the second characteristic; (d) comparing the tuples of characteristics of step (c) with a predetermined normal operating range of a multidimensional characteristic diagram which is defined at least by the first characteristic and the second characteristic; and (e) storing a tuple of characteristics of step (c) and/or triggering an alarm signal if said tuple of characteristics from step (c) is outside the normal operating range.