The purpose of this work is to develop algorithms to identify fuel cell faults using electrochemical impedance spectroscopy. This has been done to assist with the development of both onboard and off-board fuel cell diagnostic hardware.; Monitoring the impedance of a fuel cell at 50 Hz, 500 Hz, and 5 kHz can also be used to differentiate between flooding, drying and CO poisoning conditions. The real and imaginary parts, and the phase and magnitude of the impedance can each be used to differentiate between faults. The real part of the impedance has the most consistent change with each fault at each of the three frequencies. This method is well suited to an onboard diagnostic device because the data acquisition and fitting requirements are minimal.; Complete implementation of each of these methods into a final diagnostic device, be it onboard or off-board in nature, requires the development of reasonable threshold values. These threshold values can be developed through testing done at normal fuel cell operating conditions.
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