I don't want to get too nitpicky but not all (in fact, most) part-time 4wd do not have a lockable center diff (manually or automatically).
Really? Which ones? When I think part-time I mostly think of trucks. I've never had a truck, but everyone one my father has owned had a transfer case you engaged to put it in 4WD mode, and it would lock the center diff.
His last pathfinder did have AWD and 4WD... AWD would leave the center in a limited slip/active mode, 4WD would simply lock it.
Sorry, I had a momentarily lapse and you are correct.
