[scha0786]

Put the hubs in lock and if you have 4wd then you have a vacuum issue. When the hubs are placed in Auto, vacuum is NOT applied and the hubs are not locked in. When you flip the switch in the cab and vacuum solenoid opens and also vacuum to be applied to the hub assembly which pulls them in and locking them into 4wd.

Thats as much as I know from trouble shooting my old 2004 F250 which basically has the same system as my new 2019.

Now - Ford Doctor will have way more knowledge on the computer side of things of what happens within the ECU etc and maybe there is something going on electrically.

Id start with flipping the switch to 4wd high and manually putting hubs to "lock" drive forward a little bit and if you have 4wd, then you have a vacuum issue/computer. If you don't have 4wd then I would have it scanned at a ford dealership to see if there is something electrically (wiring) going on. maybe its a bad actuator on the transfer case, sensor blah blah.

 

[scha0786]

Interesting. So when I flip the switch in the cab it opens a solenoid that provides constant vacuum to the hub to lock them in?

 

[scha0786]

have you checked fuses?

Another thing you can do to help is put the hubs in auto and switch to 2wd. Go under truck and you should be able to freely spin the front axles. Once you verify that. Then switch the hub to lock and the front axle should not be able to move. Do this to both sides.

If they are still able to move then you got something mechanically going on in the hub assembly (which I have to imagine is extremely rare). If they both lock then try the vacuum gauge test.

Pull the vacuum hose off of the front hub (doesn't matter which side for now) and hook in your vacuum gauge. Start truck up, turn switch in cab to 4wd and go see if you have vacuum at both sides. If you don't then you'll have to trace the vacuum hoses up to see where the issue is.

Beyond this, its time to hook in Forscan and see what you can see.

 

[scha0786]

Are you talking about the electric motor on the transfer case?

 

[scha0786]

hmm, I'll try to remember to look tonight on mine.

Not sure why that would matter though.

 

[scha0786]

good job trouble shooting. Curious what busted in the hub, either stripped the shaft teeth or literally sheared the stub.

 

[scha0786]

I think he is past the electrical issue assumption. He snapped something in the hub assembly.