Introduction. The article presents an overview of modern diagnostic methods for mobile machines. The directions of diagnosis are outlined: with the applications of algorithms based on the use of a complex of controllers designed to collect and store up-to-date diagnostic information; with the help of artificial intelligence allowing to perform step-by-step diagnostics on current information about the speed of hydraulic motors, pressure and fluid velocity. The article also demonstrates the ways for using parametric statistical methods that are possible to determine the state of the working fluid and predict the state of various hydraulic drive units; filter condition indicators for assessing the wear degree of gear pumps; a system of indicators demonstrating unconsumed residual resource of hydraulic drive elements.Materials and Methods. The authors propose to use the Bernoulli equation to determine the velocity and piezometric heads in selected sections of the hydraulic drive in order to construct a digital model in the form of a hydraulic slope curve. It is noted that for hydraulic systems equipped with hydraulic motors, it is possible to obtain different operating modes of hydraulic sections at minimum and maximum pump speeds, which makes it capable to analyze the operation of the hydraulic system at pressures that vary over a wide range. The digital model is built on the basis of known dependencies, which theoretically allow us to determine the velocity and piezometric pressures in different parts of the hydraulic system.Results. The application of this digital model in various areas, during maintenance of the hydraulic drive and a comparison of the measured values in the sections of the hydraulic system with the theoretical ones will make it possible to establish its serviceability or predict failure.Discussions and Conclusions. The proposed approach will allow to carry out repairs in a timely manner and eliminate sudden equipment failure.