The transmission of a car is considered as a diagnostic object in this article. Significant diagnostic signs for the designated purposes are indirect (acoustic, vibrational, thermal, etc.). From the practice of operation, it is known that the vibrations that occur during the operation of a technically serviceable node, transmission unit, differ from the vibrations that occur during the operation of a failed node, as well as from a node that is in a pre-failure state. It is obvious that as the resource is exhausted, the spectral composition of the vibrations transmitted by the transmission units to the external environment changes. Consequently, by changing the spectral composition of vibrations, we have the opportunity to track the change in the technical condition of the mechanical unit from its serviceable condition up to its failure (node failure). Hardware, this can be done using built-in vehicle design, or external, specially installed vibration sensors.