Audi is following BMW by introducing a mechanism to prevent misfueling of diesel vehicles with gasoline. It's generally not possible to put diesel into a gasoline-powered vehicle as the larger diesel nozzles won't fit in the filler neck. However, the smaller gas nozzles will fit in the diesel neck. Audi's system, similar to the one used by BMW, adds a flap in the neck to prevent fuel flow. The flap only opens if the nozzle presses on contact points just below the cap. The smaller gasoline nozzle won't be be able to hit all of the contacts at once and the flap will prevent fuel from getting into the tank. Apparently, the improved refinement of modern diesel engines has led to an increase in misfueling in recent years, prompting both BMW and Audi to add the new feature. BMW has had this mechanism in all of its diesel vehicles since early 2009 and Audi's system is set to appear next year.