4wd light on but no 4wd

[Donnie]

Sometimes my 4wd will work and sometimes it won’t this is my first winter with my 2010 crew cab Laramie . When I shift it into 4wd the light flashes for a sec then goes solid but I was going up a slippery driveway tonight and got stuck only to realize my 4wd wasn’t engaged any suggestions would be great

 

[Burla]

We had someone on the board just change the dif fluid and fixed this, shot in the dark but it is likely way overdue if you haven't yet. Redline or Amsoil seams to be good options. I have the same thing with my 2010, I haven't tried it yet but will soon as well, redline 75w85 or close for front dif, 75w140 for rear.

 

[BWL]

If it's really cold sometimes the electric motor that engages the front axle won't engage on mine until the diff warms up. Not sure the solution. I just park mine in 4wd lock if I think I'll need 4wd when I drive it next if it's cold. If you haven't changed the oil in it yet it's worth checking out. Mine usually looks dirty and I change it every 20000 miles or so. if you go for a drive and then try 4wd at the end of it it may start working again.