The control system has a section for determining the reference value for the movement of the steering wheel from an estimated steering angle in place of the measured steering angle if the neutral steering angle is not known and it is not possible to determine the steering angle measured on the basis of the neutral position. The estimated steering angle can be determined by the addition of the stored steering angle at the instant the ignition was switched off, to a value which represents the steering lock which is measured after the ignition is switched on.
