Many fault-tolerant mechanisms have been proposed by software and hardware designers based on the communication protocol to ensure Steer-by-Wire system safety. The objective of this paper is to evaluate the impact of two fault-tolerance services mainly used for X-by-Wire systems, Fail-Silent Electronic Control Units and Membership Agreement, as to X-by-Wire system dependability. By creating a Failure Model adapted to X-by-Wire systems and fault tolerance properties, we give an analytical method which quantifies the impact of Fail Silent Property on the probability of an undesired event, and the impact of Membership Agreement on the probability of vehicle immobilization