Fixed my ESOF today as the auto locking hubs would not lock automatically.
Did not even know they were not working till I had gotten off the pavement artwork today after a good rain. While trying to get back on pavement, I switched the **** on the dash to 4x4 high and did not get 4x4. Noticed the front wheels not turning so I got out and manually locked the hubs and proceeded out of the mud. I know the Fords have a crappy auto locking hub system from my previous truck...a 2002 Superduty 4x4. I had actually replaced the auto lockers on the 02 with Warn Premium Hubs.
Well.. I knew I did not have a vacuum leak because my AC was not defaulting to defrost.
And I knew the vacuum pump was working because I could hear it running with the key on and feel the vacuum with my finger..Also the lines leading to the back of the hubs appeared to be in very good shape.
At this point I was thinking that I would take the hubs off the truck to clean and lube them and replace the o rings and then they should work...right?
So I went to the Dealership to see about buying a kit with new o rings in it. The parts guy there was telling me that there was a Solenoid Valve that sends the vacuum to the hubs and that he sells a lot of them to guys with the 4x4 trucks with ESOF system. He goes to the back and brings one out for me to look at and tells me that replacing it might fix my problem.
So I go out to my truck and locate the solenoid valve and find it mounted on top of the radiator on the passenger side...very easy to get at. I go in the truck...turn on key...engage 4x4 and go out to check it out.
By unplugging the vacuum lines I made the pump start up but also realized that I had vacuum at this valve but not going thru it and going back out to the hubs. Then it dawned on me that it was a little odd that both hubs would be sticking at the same time.
So I go back in and buy the Solenoid Valve (PVH SOLENOID) part no. 7C3Z-9H465-A. It was about $90.
So I took it home and it took me a whole 6 minutes to install and hoping this would fix my problem and wondering if it may have only been a fuse or something.
Anyway... Thanks to the part guy..IT WORKS!!!!
He saved me a bunch of work.
I think I owe him.
This was a little long winded but I thought I would share what fixed my ESOF.

 

Good to hear its fixed! $90 tho, sheesh!!
I still need to fix mine, broke a vacuum line under battery box. Ftr, my vacuum pump is unplugged and my hvac does not default to defrost, operates normally.