D3XL

I’m looking for some guidance here. I have a 2002 Cat D3XL open station with original 1400 hours. It has the 2 speed button on the steering controller. The machine will push dirt, move and everything works. The problem is that the machine will not go into high range when the button is pushed. The green light comes on the dash as of high range is active but nothing happens. Any thoughts or comments or guidance should be helpful.