In most cases when the auto is taken into anywhere like a dealership or where ever...if there is an update to the computer programming they will "reflash" the computer. It can be for several different reasons including emissions. This in turn can cause worse fuel mileage because it will remap how the engine uses and burns the fuel. All this new emission stuff they're putting on these vehicles are supposedly making it easier on the environment, but it's creating worse fuel mileage and we're having to refuel more often. Kind of a double negative if you ask me.
