Thank You.The AWD is "always on", but unless required (I.E slippery conditions) will only apply power to the front wheels. The button that you have in your dash is to force it to apply power to the rear wheels too, but it will disengage automatically above a certain speed.
There used to be a long thread in the sticky section that was explaining all this. A quick search should bring it right up.
Thank you.You do not want to push the awd lock button and leave it on all the time. When engaged it locks the front and rear axles to turn at the same speed. This is a bad situation to have going into a turn on solid pavement since the axles need to rotate at different speeds as they have different turning radii.