The invention relates to a method for detecting a malfunction in an electromagnetic retarder. More specifically, the invention relates to a retarder comprising: stator primary coils (8); a control unit (19) for injecting a current into the primary coils (8), said current having an intensity corresponding to an intensity set value (Ci); a sensor (21) which delivers a signal that is representative of an effective intensity value (Ie) of the current passing through the primary coils (8); and a shaft (7) bearing secondary windings (5) defining several phases and field coils (13), as well as a current rectifier (5) which is disposed between the secondary windings (5A, 5B, 5C) and the field coils (13). The inventive method consists in comparing the intensity set value (Ci) and the effective intensity (Ie) in the control unit (19) in order to identify a fault in the event that the intensity set value (Ci) and the effective intensity (Ie) differ by an amount greater than a threshold value. The invention is suitable for electric retarders (1) which are intended for heavy vehicles, such as trucks or other vehicles.