Wheel Motor Electric Bus (W.M.E-Bus) is a recent e-mobility technology, which has a complex system integration. Since the operational reliability and life cycle data of such systems is scarce, it becomes impractical to plan for maintenance and determine system-critical components. Moreover, E-Bus system dismantling and assembling is a long time process especially for components near to the its Power-system. In this paper, we propose a Fuzzy-logic fault-tree evaluation for the W.M.E-Bus system under uncertain failure data. The proposed method indicates the critical components that significantly influence the system's failure uncertainty. At 10% failure rate uncertainty, control unit failure, including the embedded software, is ranked the top critical failure mode with 1.8 Fuzzy Importance Measure (FIM).