The aim of the study is to increase the efficiency of operation of underwater vehicles (UVs) by using systems of functional diagnosis of their thrusters, by providing detection, localization and identification of minor faults. To solve this problem, the article proposes a new method containing two main stages. At the first stage, a bank of diagnostic observers is built to detect and localize emerging faults. At the same time, each observer is constructed according to a special procedure in such a way to be sensitive to different set of possible faults. At the second stage, additional ob-servers working in the sliding mode are synthesized to accurately estimate the fault values. At the same time, in contrast to existing solutions, it is proposed to use a reduced (having a smaller di-mension) model of the original system when constructing these sliding mode observers. This makes it possible to reduce the complexity of the obtained observers in comparison with the known methods, where full-order observers are built. The results of the research showed the efficiency and high quality of all synthesized observers. In all the considered cases, it was possible to detect the occurrence of typical faults, as well as to ensure the identification of their values. Highly reliable UV control systems can be created on the basis of the considered method.
