I have a 2006 F-250 4X4. The transfer case goes into 4X4 Hi/Lo when the switched is moved, however the hubs won't auto lock. They will lock manually without a problem. I checked the vacuum at each hub when switching to 4 Hi and no vacuum is present. The owners manual doesn't have much information.

Can someone assist? I'm looking for a system schematic or a link to one. There also must be a vacuum pump and some type of solenoid to activate it; where are those parts located? How about a fuse? fuse number?

Any help would be greatly appreciated.

Thanks in advance...

 

Sir...do a search for "ESOF" in this section. Tons of info to read. I guarantee you'll find your problem.

 

All fixed. Here's what I did:

1) Made sure the vacuum pump and the reservoir were working by just making sure it stopped running a few seconds after the key was put in to the run position and that it didn't cycle.

2) Disconnected the vacuum line from the solenoid and connected a vacuum gauge to the solenoid, switched to 4Hi and watched. Once the dash light illuminated the gauge went to 12 in.Hg for about a minute. When switched back to 2Hi and the dash light went out, I got about 7 in.Hg for about 15 seconds.

3) Connected a hand held vacuum pump ($23 from Harbor Freight) to the line coming off the solenoid, tried to pump it up -- nothing.

4) Isolated the left/right sides by capping one side of the "Y" fitting located under the vehicle.

5) Pumped it up, held 15 in.Hg for about a minute -- Left side good

6) Isolated to the right, Pumped it up -- nothing

7) Looked for a damaged line didn't see anything.

8) Connected the hand held vacuum pump to the right side hub, pumped it up -- Good (hub is not leaking)

9) Replaced vacuum line from right side hub to "Y" connector.

10) Tested -- All good

Found a small pin hole in the right side vacuum line halfway between the "Y" connector and the hub.

System Repaired (total cost = $12.89)