One of the important standards of technical operation of motor vehicles is the frequency of their maintenance. The correct definition of it directly affects the amount of specific operating costs and is one of the most important tasks of engineering and technical workers. At the same time, their reduced values, although they lead to an increase in the reliability of vehicles, but they increase the frequency of downtime and the cost of operation, as well as increase the share of unused resources of serviced systems and mechanisms. In this paper, we consider an economic-probabilistic method for determining the frequency of maintenance. There are two tactics for implementing this method: by operating time and by technical condition. For all its simplicity, the method of determining the operating time has a number of disadvantages, namely, it does not take into account the technical condition of the serviced mechanisms and units at the current moment. This increases the complexity of performing maintenance operations, and their cost increases accordingly. The method of determining the frequency of maintenance by condition is considered. In this case, all work on the maintenance of mechanisms and aggregates of vehicles is divided into diagnostic and executive components. At the first stage, their technical condition and resource are determined until the next scheduled maintenance. If this resource is not enough to run before this event, then a decision is made to perform the executive part of the work. With a larger resource, the executive part is postponed until the next scheduled maintenance. The determination of the frequency of maintenance is based on the results of comparing the specific operating costs for routine repairs with the weighted average costs for maintenance and routine repairs.