The decoupling of the current sweep with the Ohmic resistance is a very powerful tool to determine the magnitude of the voltage losses inside of a fuel cell. In a time frame of seconds, the fuel cell can be diagnosed and critical information on the state of the membrane, catalyst and diffusion layer can be assessed. The losses determined by this technique are the Ohmic, mass transport and activation. With this technique flooding and dry can be isolated and degradation studies can be made. Finally, this technique can be applied to a real system were this data can be used to improve control strategies for performance and durability when integrated in to a model based controller.