— Many reasons may cause malfunction of a proton exchange membrane fuel cell stack. Moreover, a single defect cell can affect the whole stack functioning, therefore the localization of this cell is crucial as well as identifying the root causes for such malfunctioning. The diagnosis tool has to be non intrusive and to be easy to replicate to a new fuel cell system. This paper explores paths to achieve such monitoring based on the use of the magnetic field induced by the fuel cell stack internal currents. Designing and using a three–dimensional simulation tool allows to establish a cause and effect relationship between fuel cell defects and specific magnetic signatures. This preliminary work enables to determine the required magnetic sensor accuracy, the sensor orientation and location as well as the experimental precautions for relevant measurements. Index Terms— Proton exchange membrane fuel cell; Maxwell-Stefan diffusion; magnetic field; 3D PDE modeling, diagnosis. I. AIM Using polymer electrolyte membrane (PEM) fuel cells (FCs) is an attractive way to produce energy without greenhouse gas. A defect in the FC stack, such as drying, flooding, starvation, active layer deterioration, induces major negative effect on the operation of the overall energy conversion system (FC and its auxiliaries): performance decreases and may cause the FC system to shut down, with possible damages to the PEMFC or to one of the auxiliaries. Identification of the defect and understanding the physical processes involved are essential to diagnose accurately the reduced performance causes. The aim of this work is to compute the magnetic field created by a PEMFC in order to identify a specific signature in case of malfunctioning cell. II. PEMFC MODELING