Abstract: An apparatus and methods for detecting and identifying faults in a fuel cell are disclosed. An impedance spectrum relating to the fuel cell is compared with fault criteria to identify fault conditions in the fuel cell. A time-varying current is drawn from the fuel cell at a selected frequency and the impedance of the fuel cell at the frequency is measured. This may optionally be repeated at a range of frequencies or at combinations of frequencies to provide an impedance spectrum across the range of frequencies. The fault criteria identify one or more fault conditions that may be identified by comparing the measured impedance spectrum to the fault conditions.