The steer-by-wire (SbW) system is seen as the next generation of vehicle steering system. However, there is a possibility of system failure, and it is not yet clear how failure modes will impact driving behaviour. This work studies the impact of different SbW failure modes on driving safety. Firstly, potential failure modes in the SbW system were identified with the help of a hazard and operability (HAZOP) study. Secondly, a physical model based steering force feedback, with the possibility to simulate the failure modes, was implemented in Matlab/Simulink. Third, two test scenarios were constructed, including driving on a country road at 70 km/h and driving on a highway at 110 km/h. Additionally, a driver-in-the-loop experiment was performed using a stationary driving simulator, where subjective and objective data was collected. Then, in terms of result analysis, both subjective and objective evaluation methods were used for severity assessment. Finally, the result of the severity analysis in the form of yaw rate is shown.