OK, having issues here. My first Wrangler. I can't get the rear locker to lock in 4 high. Went right by the book, put it in 4H, turn off the traction control, press down on the rear locker switch, icon on dash flashes several times but does not lock. I can go to 4 low and get both axles to lock but not the rear in 4H. What am I not doing?