An automated method or procedure for detecting a permeability state of a membrane of a fuel cell stack is provided. The procedure is sensitive enough to detect a defective membrane, and is accurate enough to enable correct maintenance of the fuel cell stack. The fuel cell stack is formed of a stack of electrochemical cells each having an anode and a cathode sandwiching a polymeric ion-exchange membrane therebetween. The fuel cell stack includes a fuel gas supply system on the anode side of the electrochemical cells, and includes an oxidant gas supply system on the cathode side of the electrochemical cells.