Method for detecting a fault in a motor arrangement with an electrical machine, particularly a synchronous motor, having the steps of: - ascertainment of rotation angle data that, in the absence of the fault, are dependent on a rotation angle of a rotor of the electrical machine by measuring a value of a sensor signal from a rotation angle sensor and by calculating a rotation angle based on the measured value of the sensor signal; characterized by - ascertainment of additional data (S10-S19) that allow the fault to be inferred, wherein the step of ascertainment of additional data comprises the step of ascertainment of a first and second speed (S13, S18) of the electrical machine on the basis of the ascertained rotation angle data, the step of ascertainment of the first and the second speed of the electrical machine comprises the steps of: • ascertainment of first rotation angle data, • waiting for a predetermined first period of time, • ascertainment of second rotation angle data, and • ascertainment of the first speed on the basis of the first and second rotation angle data and also the predetermined first period of time, • waiting for a predetermined second period of time, • ascertainment of a second speed, • ascertainment of a rate of change of the ascertained speeds as the additional data on the basis of the first and second speeds and also the predetermined second period of time, and • checking whether the ascertained rate of change meets a second criterion, namely whether the ascertained rate of change exceeds a predetermined rate of change threshold value; and - detection of the fault when the rotation angle data meet a first criterion and the additional data meet a second criterion, by checking whether the rotation angle data meet the first criterion, and, if the rotation angle data meet the first criterion, by checking whether the rotation angle data are constant; - wherein the first criterion is met when the rotation angle data correspond to a predetermined rotation angle, and the second criterion is met when the ascertained rate of change exceeds the predetermined rate of change threshold value. - ascertainment of rotation angle data that, in the absence of the fault, are dependent on a rotation angle of a rotor of the electrical machine by measuring a value of a sensor signal from a rotation angle sensor and by calculating a rotation angle based on the measured value of the sensor signal; - ascertainment of additional data (S10-S19) that allow the fault to be inferred, wherein the step of ascertainment of additional data comprises the step of ascertainment of a first and second speed (S13, S18) of the electrical machine on the basis of the ascertained rotation angle data, the step of ascertainment of the first and the second speed of the electrical machine comprises the steps of: • ascertainment of first rotation angle data, • waiting for a predetermined first period of time, • ascertainment of second rotation angle data, and • ascertainment of the first speed on the basis of the first and second rotation angle data and also the predetermined first period of time, • waiting for a predetermined second period of time, • ascertainment of a second speed, • ascertainment of a rate of change of the ascertained speeds as the additional data on the basis of the first and second speeds and also the predetermined second period of time, and • checking whether the ascertained rate of change meets a second criterion, namely whether the ascertained rate of change exceeds a predetermined rate of change threshold value; and • ascertainment of first rotation angle data, • waiting for a predetermined first period of time, • ascertainment of second rotation angle data, and • ascertainment of the first speed on the basis of the first and second rotation angle data and also the predetermined first period of time, • waiting for a predetermined second period of time, • ascertainment of a second speed, • ascertainment of a rate of change of the ascertained speeds as the additional data on the basis of the first and second speeds and also the predetermined second period of time, and • checking whether the ascertained rate of change meets a second criterion, namely whether the ascertained rate of change exceeds a predetermined rate of change threshold value; and - detection of the fault when the rotation angle data meet a first criterion and the additional data meet a second criterion, by checking whether the rotation angle data meet the first criterion, and, if the rotation angle data meet the first criterion, by checking whether the rotation angle data are constant; - wherein the first criterion is met when the rotation angle data correspond to a predetermined rotation angle, and the second criterion is met when the ascertained rate of change exceeds the predetermined rate of change threshold value.