There are a few things that could cause this. I have read about a few on this forum, from a simple faulty switch or similar, to a problem in the rear end itself. Mine went on because a clip in the rear end broke, so the truck thought the diff was locked all of the time. The dealership replaced my whole rear end. Nissan makes it as an assembly, rather than having replaceable parts. Luckily mine was under warranty.
k&n fipk cold air intake, hypertech max energy programmer, banks monster exhaust 3". daystar 2"/2" lift. toyo open country at2 265/75r16. kicker zx700.5 5 channel amp, pioneer ts-d691r 6x9" and ts-d161r 6-1/2" speakers, 12" rockford fosgate punch p3 sub in a sealed box. custom mounted 36" knaack box or aluminum utility cap(depending on the season), custom pressure treated platform with removable center panel(to fit 4x8 sheets in the bed), weathertech floor liners.
still to come; tjm leaf packs, and shocks, tjm extended travel coilovers, uca, 16x8.5 wheels or 1-1/4" wheel spacers, n-fab nerf bars or rock sliders, intake manifold spacer, lightweight crank pulley, e-fan, plasti-dip chrome.