The paper reports on the influence of low humidity, short-circuiting, hydrogen starvation and open circuit potential on the performance and service life of 11 kW PEFC stack and 25 cm(2) single cell. The failure modes in PEFC stack were caused by series of laboratory and software shortcomings during the tests, while tests in a single PEFC were performed for comparison purpose. Due to the impossibility to predict the influence of the failure modes on PEFC stack performance and durability based solely on the results obtained in a single PEFC demonstrated in the paper and having in mind the cost of a high power PEFC stack there is a lack of systematic knowledge in the field. The failure modes' influence was investigated in detail on the performance of the overall PEFC stack, individually on each membrane electrode assembly (MEA) in the stack and on the single PEFC. The reasons for MEAs failures were explained and recommendations for PEFC stack rehabilitation were given. By analyzing the reasons and shortcomings causing the failure modes the paper also provides information on some specifics in coupling and communication between some conditioning and testing devices. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.