The fault detection problem is studied in this paper for a class of linear networked control systems (NCS) with communication delays. The aim is to generate residual signals which, in the fault-free case, are supposed to be identical to zero. In practice, this condition is not respected due to various factors such as measurements noises, model uncertainties, and in particular for NCS communication-induced delays. In this work, the communication delays are described as a random Markov jump process and a fault isolation filter is developed. Directional residuals, decoupled from the disturbance, are generated to ensure the treatment of multiple faults appearing simultaneously or sequentially. The parameters of the filter are determined to satisfy H ∞ disturbance attenuation and poles assignment constraints in the frame of Markov jump linear systems. Sufficient conditions for the existence of the fault detection filter are set in terms of linear matrix inequalities. An illustrative example is given to show the efficiency of the proposed method for NCS.