There were analyzed current modernization areas of locomotives powerful diesel generator sets (DGS). It was determined that to improve the efficiency of the DGS, it is necessary to modernize the speed and load controllers. Three methods of their modernization are considered. It was determined that the most effective method to increase the profitability of locomotives is the introduction of electric speed and power regulators with the ability to control the start of fuel supply. Also, a significant increase in efficiency can be achieved by reducing the frequency of idling, but it is necessary to take into account a number of limitations. Theoretical studies have shown that the application of the proposed methods to reduce the average cost of fuel per unit of time in the thrust mode for steady-state and transient conditions, the efficiency of a diesel generator can increase by 4-5%. A huge impact on the final indicators of reducing fuel consumption in operation has the skill level of the staff and the technical condition of the diesel generator set, as well as the degree of workload. The results of theoretical studies were confirmed by tests results that had been carrying out under actual operating conditions for a year in Kharkiv, Ukraine.