A method for determining a failure of a membrane in a fuel cell in a fuel cell stack. The method includes measuring the voltage of each fuel cell in the fuel cell stack, calculating an average cell voltage from all of the cell voltages of the fuel cells in the fuel cell stack, and identifying a minimum cell voltage from all of the cell voltages of the fuel cells in the fuel cell stack. The method then determines an absolute delta voltage value as the difference between the average cell voltage of the fuel cells and the minimum cell voltage of the fuel cells at a plurality of sample points during the sample period. A plurality of absolute delta voltage values determined over a plurality of sample periods, filtered for low current density are used to determine whether there is a membrane failure and, by filtering for high current density, to determine whether there is an electrode failure.