In this study, a model based diagnosis of a hydrogen-fueled 1-kW proton exchange membrane fuel cell (PEMFC) system was conducted based on exergy analysis to identify faulty components. Faulty components of balance of plant (BOP) were experimentally simulated by reducing the rpm signals of the pump, fan, and air and fuel blowers; reducing the output signals of the air and fuel flow meters; increasing the output signal of the temperature sensor; opening the valve between the air blower and the air flow meter; and blocking the heat exchange area during the operation of the PEMFC system. The irreversibility rate, malfunction (MF) and dysfunction (DYS) of each component were calculated for the case under normal condition and simulated failure conditions using the observed data. The residuals of the MF and relative malfunction (RMF) between the normal and failure conditions were the fault indicators used to identify the faulty components in the system. The proposed diagnosis method employing both the MF and the RMF was found to be not only simple but also effective. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.