A method of performing real-time sensor diagnostics on a subcutaneous or implanted sensor having at least one working electrode, comprises (a) performing a first electrochemical impedance spectroscopy (EIS) procedure to generate a first set of impedance-related data for the at least one working electrode； (b) after a predetermined time interval, performing a second EIS procedure to generate a second set of impedance-related data for the at least one electrode； and (c) based on the first and second sets of impedance-related data, determining whether the sensor is functioning normally. The first and second sets of impedance-related data can include data for at least one impedance-related parameter that is substantially glucose- independent, for example imaginary impedance measured at a frequency of at least 1kHz.
