Ford shift on the fly - no 4HI

austinjenna wrote:
2010 F-360 6,4L
My electronic shift on the fly will not engage in 4 HI. It will go into 4 low, comes back out into 2HI just fine, just no 4HI. I can manually lock the hubs and it will work, just not from the dash switch. The light on the dash does come on as well if I use the shift on the fly.

Since I can manually lock in the hubs and it works I have eliminated the hubs. I tried the defrost/vent trick and it works as it should. I know these things work on vacuum and since its going into 4low I can eliminate a vacuum leak. Im just trying to debug it before going to the dealer.

Any ideas on where to look?

How are you determining 4 low is working but 4 high is not? I'm assuming that you are feeling it go into low range is why. You won't be able to tell if the transfer case is shifting into 4 high because the speed range don't change. The only other way to tell is look under the track to see if the front drive shaft is turning while the truck is moving. Do this with the hubs in the unlocked or auto position. Fords are bad about the vacuum hubs quitting. The transfer case will shift but the auto hubs won't engage. Have you shifted the hubs manually and then tried getting on a loose surface in 4 high and spinning your wheels?