Abstract: The invention relates to a method for diagnosing operating states (36, 38, 40, 42) of a synchronous pump in a liquid circuit, particularly in a washing machine or similar. According to the inventive method, the alternating voltage (U) applied to the pump motor and the alternating current (1) of the motor are measured in at least one measurement step (30), the extent of a phase shift (??) between the alternating voltage (U) and the alternating current is measured at least at one point in time in a determination step (32), the phase shift (??) or the progress thereof is determined from the recorded measured values and a characteristic of the phase shift (??) or the progress thereof is determined, and the determined characteristic is assigned to a predetermined pump operating state (36, 38, 40, 42) in an assignment step (34).