a system and method for detecting soot and or ash loading within a filter is provided . the method comprises the steps of transmitting a source rf signal through a filter , measuring a reflected rf signal , measuring a transmitted rf signal , calculating reflected power by comparing the source rf signal with the reflected rf signal , calculating attenuated power by comparing the source rf signal with the transmitted rf signal , and determining soot loading based on reflected power and transmitted power . the system and method may also determine ash loading .