The paper deals with a fault-tolerant extension of an existing steering angle sensor used for future steer-by-wire applications in automotive areas. In our approach fault tolerance is added to the sensor in two ways. On the one hand it is achieved by exploiting some basic properties of the mathematical relations on which the calculation of the steering angle of the steering column is based. On the other hand two optical sensing elements are used in addition. Hence, we gain fault tolerance by redundancy and, concurrently, by diversity because of the different physical sensing principle. By means of fault injections and several scenarios for turning the steering wheel, fault simulations were carried out in order to evaluate the diagnostic properties of the sensor.