Fast and large-angle attitude slew maneuvers often imply simultaneous use of multiple actuators such as thrusters and reaction wheels (RWs). A fault in any of these actuators might lead to partial or full damage of sensitive spacecraft instruments. In this paper, a model-based Fault Detection and Isolation (FDI) strategy is proposed, which aims at detecting various actuator faults, such as stuck-open/closed thruster, thruster leakage, loss of effectiveness of all thrusters, and change of RW friction torque due to change of Coulomb and/or viscosity factor. The proposed FDI strategy is also able to detect and isolate faults affecting the RWs tachometer sensor. The FDI system design is based on a multiplicative extended Kalman filter and a generalized likelihood ratio thresholding of the residual signals. The performance and robustness of the proposed FDI strategy is evaluated using Monte Carlo simulations and carefully defined FDI performance indices. Preliminary results suggest promising performance in terms of detection/isolation times, miss-detection/isolation rates, and false alarm rates.