I have an 07 which I bought used and the front wouldn't engage.
First thing you should rule out is the switch. Make sure you have voltage going to the diff.
The next easiest thing is to replace the fluid. The front is a bit finicky if it has the wrong fluid or it got water in it.
If, however, you jack the front up and spin the yours by hand and there is binding or grinding noises probably the cage inside is broken. I remember it being a relatively inexpensive part and a relatively easy job to replace.
Either case if you don't have binding and don't want to take the diff apart, I would definitely try replacing the fluid.
Good luck