The effects of local gas diffusion layer (GDL) gas permeability variation and its location on spatial and overall proton exchange membrane fuel cell (PEMFC) performance were studied using a segmented cell approach. Variations in the physical and chemical parameters of the main membrane electrode assembly's (MEA) components (e.g., the membrane, electrode, and GDL) are considered defects and might negatively affect fuel cell performance. An artificial GDL defect was introduced by exchanging a standard (or intact) cathode GDL at one segment (segment 4 or 9) with a defective GDL. The standard and defective cathode GDLs had different through-plane gas permeabilities, while values were similar for in-plane permeability and some other structural parameters. The effects from a defective GDL were observed at a high current. Introducing a highly permeable GDL as a defect increased local performance due to a decrease in mass-transfer overpotential. For a defective GDL with lower permeability than the standard GDL, a local performance decrease was observed because mass-transfer losses increased. Simultaneously, downstream segment performance improved, which might be due to changes in water management. Defect localization at the cell outlet resulted in the detection of the defect at a lower current density compared with localization at the cell inlet. Spatial polarization curves (VI) and electrochemical impedance spectroscopy (EIS) facilitated detection and localization of GDL defects. Thus it was demonstrated that the local GDL anomalies are detectable by the segmented cell system. (C) 2013 Elsevier B.V. All rights reserved.