The paper deals with the reasons for the failure of the motor-reducer from the drive and measures to extend its service life. The motor-reducer as an element of the electric drive is widely used in all areas of industry. At the rated load, usually recommended by the manufacturer, the gearbox has its own service life, which is significantly reduced under operating conditions with the maximum permissible load. The attack detection problem is considered as fault detection problem. An observer-based fault detection method for DC-motor with reduction gear is proposed. Simulation results are given.