The article discusses a way to increase the efficiency of automobile operation by improving methods for ensuring the operability of electrical equipment based on the diagnosis of generators by output voltage. As a diagnosis, it is proposed to perform a spectral analysis of the generated voltage in idle mode and to determine the state of various generator elements from the results. The effectiveness of the proposed solutions is determined by the non-separable diagnostics of the generator, which, based on a thorough examination, can determine the state of various elements of the generator. This method does not require taking the generator out of operation, does not depend on its design and can be used in difficult operating conditions to obtain preliminary information about the state of the generator at the initial stage of maintenance.