In a device for diagnosing a mechanical system driven by an electric drive motor, the drive motor thereof, and the shifting device thereof include at least one sensor for detecting the current curve in a conductor of the electric connection of the drive motor. The precision and the degree of detail of the diagnosis are to be improved compared to the prior art and expanded to include the drive motor and the shifting device in order to improve the efficiency and aim of the maintenance process carried out in response to the diagnosis. This is achieved in that the device additionally has sensors for detecting the voltage curves in the conductors of the electric connection of the drive motor, wherein each conductor is paired with a sensor for detecting the current curve and with a sensor in interaction with a sensor in order to detect the voltage curve.