This paper introduces fault diagnosis and separation, mitigation, and modeling of a proton exchange membrane fuel cell (PEMFC). Experimental tests of a single PEMFC were performed during this study. Flooding and drying faults were implemented to be detected from the cell voltage and impedance response of the cell. The impedance response at low frequency was used to identify the cause of the fault. The slope of the magnitude and/or the negative phase response of the cell impedance at low frequency were observed to allow separation of a fault. A cell impedance model based on resistive capacitive (C model) and resistive constant-phase-element (CPE model) circuits is developed. The CPE model has a better approximation of the cell impedance. However, the C model is easy to implement since it is well known in most simulation tools (MATLAB/Simulink or PSpice). A power electronic control is designed and tested to mitigate the faults. Pulsing the cell current at low frequency was seen to increase the cell power by 8% during drying. © 2010 IEEE.