Abstract: A system and method for identifying leaks in a cathode sub-system of a fuel cell system. An air flow meter is provided up-stream of a compressor and monitors the air flowing into the compressor. When an air leakage diagnostic is commanded, a fuel cell stack by-pass valve and back-pressure valve are closed so that no air flows through or around the stack, and the recirculation valve is opened so that the air flows around the compressor. By knowing the leakage through the by-pass valve and the back-pressure valve, any flow above those values measured by the air flow meter gives an indication of air leakage out of the cathode sub-system components.

Abstract: An engine control system for a vehicle includes a flowrate module, first and second mass fraction calculating modules, and an actuator control module. The flowrate module determines a mass flowrate of exhaust gas recirculation (EGR) to an engine. The first mass fraction calculating module, based on the mass flowrate of EGR, determines a first mass fraction of recirculated exhaust gas relative of a first gas charge for a first combustion event of the engine. The second mass fraction calculating module determines a second mass fraction of recirculated exhaust gas of a second gas charge for a second combustion event of the engine based on an average of the first mass fraction and one or more other values of the first mass fraction determined for other combustion events, respectively. The actuator control module selectively adjusts an engine operating parameter based on the second mass fraction.