The electric servo steering system has an electric motor whose torque is added to the steering torque by a control programme in response to steering torque and steering deflection setting. The control programme has two operating modes; one for normal control and one for a backup control. If a failure is detected e.g. if the steering setting sensor is faulty, the failsafe control switches to the backup mode. This ensures that the driver does not experience a sudden change in steering resistance.
