A diagnostic system for a resolve of a motor and a method of diagnosing the resolver. The diagnostic system includes an x-phase winding, a y-phase winding, and a processor. The x-phase winding generates an x-phase voltage and the y-phase winding generates a y-phase voltage. The processor obtains the x-phase voltage and the y-phase voltage, determines an adaptive cosine envelope from the x-phase voltage and an adaptive sine envelope from the y-phase voltage, determines an adaptive magnitude from the adaptive sine envelope and the adaptive cosine envelope, determines a magnitude average based on the adaptive magnitude, determines a fault of the resolver when a ratio of the adaptive magnitude and the magnitude average is greater than a threshold, and transmits a signal based on the fault.