Pressure decay test is usually used to highlight leakages inside the stack between anode, cathode and cooling compartments. Although this test can satisfactorily detect leaks occurring within the stack, it does not help in localization of the leak source in the stack. This paper presents some descriptions of two PEMFC stacks which have leakage between anode/cathode or cathode/cooling compartments. A variety of diagnosis techniques including IR thermography, Open Circuit Voltage decay, Crossover Current, Open Circuit Voltage growth are employed with the goal to locate the leak sources in the stacks. Furthermore, some techniques are presented to find the leak types and sources in the defective cells in the stack. Since hydrogen and air are not used simultaneously in the stack, the crossover current test is safer than the other methods. However, results of this test are strongly dependent on the nitrogen flow rate. The results of IR thermography show that this technique has a good potential to be used along with the other methods in the leak diagnosis of the PEMFC stacks. In fact, this technique can be used to build confidence in the results of the other leak diagnosis techniques. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.