A system and method for detecting a failure in a redundant signal path during operation of the redundant path is disclosed. A test signal is sequentially injected into each signal path while an input signal is conducted by the other signal path not receiving the test signal. The test signal is selected at a frequency to verify operation of a filter connected in series along each path. A processor generates the test signal, injects the test signal at the input of the filter, and receives the output of the filter. The processor then generates a frequency response of the filter in each signal path as a function of the output from the filter and of the original test signal. The frequency response obtained along each of the redundant signal paths is compared to each other to detect a failure of one of the filters present along the respective signal paths.