Fault estimation plays an important role in the fault diagnosis system since provides information about the fault magnitude and temporal evolution. In this paper, we present an approach that allows to obtain a simultaneous estimation of the fault, state and associated uncertainty intervals of a uncertain Takagi-Sugeno (TS) system. The fault estimation is obtained using a TS interval observer augmenting the system state with the fault and considering the system uncertainty in a bounded context. A set of Linear Matrix Inequalities (LMIs) have been derived to design the TS interval observer. With the purpose of illustrating the performance of TS interval observer for fault and state estimation, a case study based on a Proton Exchange Membrane (PEM) fuel cell is used.