from what i understand of it it's nothing you can just switch on your own... it's a built in feature and controlled by the ECM.

i think it's kind of stupid, it says that it just closes off the valves completely to shut down the cylinders; but that would mean that the engine is working really hard against pumping the closed cylinders up and down. maybe i'm just reading it wrong but wouldn't it be better to shut down fuel supply/spark to those cylinders and have the exhaust valve open still on the "exhaust" stroke of those cylinders to eliminate some of the pumping losses and further improve mileage?