A closed system such as a TET system in which self-testing of all components of the implantable medical device whose malfunction could negatively impact on the proper operation of the closed system is automatically and periodically performed without triggering from an external device. In addition, a closed system including automatic, periodic self-testing of the implantable medical device in which, whenever practical, testing of the components is synchronized with telemetric communication of the external device whereby an external RF field generated by the external device is used to supply necessary power to perform self-testing.