This recommended practice is intended to serve as a procedure to verify the functional performance, design specifications or vendor claims of any PEM (Proton Exchange Membrane) type fuel cell stack sub-system for automotive applications. In this document, definitions, specifications, and methods for the functional performance characterization of the fuel cell stack sub-system are provided. The functional performance characterization includes evaluating electrical outputs and controlling fluid inputs and outputs based on the test boundary defined in this document. In this document, a fuel cell stack sub-system is defined to include the following: Fuel cell stack(s) - An assembly of membrane electrode assemblies (MEA), current collectors, separator plates, cooling plates, manifolds, and a supporting structure; Connections for conducting fuels, oxidants, cooling media, inert gases and exhausts; Electrical connections for the power delivered by the stack sub-system; Devices for monitoring electrical loads; Devices for monitoring cell voltage; Humidification devices; Instrumentation for detecting normal and/or abnormal operating conditions; Enclosures (that may qualify as pressure vessels), and ventilation systems for the enclosure. Not included in the sub-system are the following: Fuel and air processors; Thermal management system; Power conditioner and distributor; Controllers