Hello all,
I recently acquired another F-250. This time I got a 2006 Crew Cab with the 6.0 diesel. Only 89k miles and excellent service records. This is the first diesel I have ever owned so I am sure I will be reading posts on this forum quite frequently.

One of the problems I am currently having is with the 4 wheel drive not engaging. I have read a lot of threads and used the troubleshooting but have not had any luck yet.

THE PROBLEM: I turn the switch to 4 wheel (Low or high) and nothing happens. No light on the dash, no 4 wheel engagement, I don't even hear the pump running. First thing I did was the blower test (air on mid-level setting, flipped the 4wd switch, air stays at mid level and does not default to defrost). Then I looked over all the lines and visible wiring for any obvious damage (frays or cracks) and found nothing. Following the advice from another post, I pulled the covers off the relays, turned the key on, and press the relay contacts. When I do this I am able to switch into and out of four wheel drive (confirmed by test drive) but still do not get any 4WD lights on the dash. At this point I am leaning towards a new switch since it does not seem the pump is running. My assumption, based on the fact that I do not have any heating/AC problems is that the pump is good. Or did I mistake what I have read in one of the hundreds of posts I read? I have called my local dealer and they will have a switch for me in tomorrow morning (4/10/18) for $70.05 But any words of wisdom to support or debunk my logic would be greatly appreciated. I don't want to waste the $70 if its not likely the problem.

Thanks
Ken

 

 

Yes I am absolutely sure as I have driven the vehicle on the road and in the woods and 4wd does not engage with the auto method (by turning the switch) and yes, the hubs are in auto.

 

I bought the truck from a used car dealer who has no idea of the real history of the vehicle. It seamed his mechanic barely checked the truck out, just cleaned it. I identified the inoperative sliding rear window, sunroof, and seat heater as well as the missing jack, and a door reflector. He fixed all those items. I failed to notice the 4x4 problem and that the spare tire is blown out.

 

 

I swapped the switch out this morning. No luck. Still have the same problem...

 

You still need to confirm that locking the hubs manually works. This may not be an electrical issue.

 

By bypassing the switch and going straight to the control relays and manually pushing the contacts I am able to put the truck in 4 wheel drive as confirmed with a test drive (as noted in my original post) since I am able to engage 4WD that way I know my hubs are not the problem. Or am I mistaken?

 

Bypassing the switch as descibed also did not give me a 4WD light on the dash. How do I know I was in 4WD? I know I was in 4LO because I could not go over 30 mph and my tires were tearin off on pavement.

 

The hubs are (as you know) notorious for failing to work in auto. I think you should work two paths.
First, the vacuum pump and hub relay are simple things to isolate, and not really needed for 4x4. Set those aside for a minute, and don't even think about the hubs until the real problem is solved. The real concern is if the transfer case is shifting into 4. I would:
1. Select 2WD (and roll fwd a few feet to make sure if you're shifting directly out of 4)
2. Disconnect the vacuum hub relay electrically. (Passenger side, electrical connection easy to pull off).
3. Make sure both hubs are in auto and unlocked. Reach behind the tire and roll the U-joint on both sides. They should roll by hand. If you can't turn one of them, the hub is actually locked. Move the auto-manual hub back and forth several times while wiggling the U-joint until it spins. Both sides! Now, both hubs are unlocked and won't lock on their own.
4. With the truck in park, reach under and spin the front driveshaft by hand. This should confirm the T-case is in 2WD.
5. Start truck, shift switch to 4Hi (hubs unlocked). Drive fwd/back a few feet to make sure it engages. Put truck in park.
6. Reach under and spin forward driveshaft again by hand. It should not move if the T-case is in 4. If it spins, T-case is still in 2.

if you're still in 2WD, troubleshoot switch to transfer case.
If it is in 4, repeat in and out a couple times and see if the fwd driveshaft will roll by hand. If you can be confident it is actually switching the T-case into 4 (even without a light), then you're doing good. Troubleshoot the light. You actually have 4WD.

Once you have consistent T-case shifting, then go back to the hubs. Pull them off (very easy), clean and grease them. Again, don't even need vacuum system, as you can operate the hubs just like manual hubs if you have to.

 

Thanks. I'll try that once i get to my garage.

I pulled and reseated the 30a ESOF breaker under the hood. Then flipped the switch to 4hi. For the first time I witnessed the pump is running, but I was still unable to get 4wd.

I'm on my way now to pick up a vacuum pump, figured I should check the lines.

 

 

Tusks, I'll try it. Wish I had a theory of operation video or book and a wiring diagram. A good understanding of the systems operation makes troubleshooting much easier.

 

YouTube has a bunch of videos on removing and checking the hubs. Pages and pages of videos. Worth a watch.
My recommendation, though, is forget about the hubs and solve any T-case problems and switch problems first. Don't worry about the vacuum pump. It does not necessarily always run when shifting the hubs. There is a large vacuum reservoir just aft of the pump that can just about shift the hubs on its own.
To test the vac pump, turn the truck on (do not start). Shift the HVAC controls from vents to defrost, wait a second, shift back, repeat. The vacuum pump should pick up, pull the reservoir back down, and turn off. If your HVAC controls are working, then your vacuum pump is fine. The vacuum pump is not electrically connected to the 4x4 system at all. It simply runs when the vacuum gets low, and shuts off when it gets back to near full vacuum.

 

okay so this morning I put the truck completely up on jacks. I put the hubs only in lock and when I turn either wheel I can see the forward drive shaft turn. I then placed the forward hubs in Auto and tested each Hub separately using a vacuum pump. Again I witnessed the four wheel drive shaft turn when I spun each wheel. I reconnected the hubs and plug my vacuum pump in at the solenoid and both hubs locked. (again verified by turning each wheel and observing the forward drive shaft spinning). Disconnecting the line from the solenoid also depressurize the vacuum and the pump turned on. As stated previously, if I manually depress the contacts on the esof control relays my transfer case will shift into and out of 4 wheel drive. Since I already changed the switch I turned my attention to the 4x4 control module that should be above the glove box. However I have no 4x4 control module, just two connectors that go to nothing. I called my Ford dealer and they say based on my VIN number that they cannot find a 4 x 4 control module in their books. I've seen other posts that say this module was removed in 2002 or 2003 with those functions being transferred to the cluster and other components. But then why do I have connectors?
​​​​​​Should I have a 4 x 4 control module installed above the glove box? Another tidbit of information, I just bought this truck and it was listed as a "theft recovery" so it's possible if there was a control module, this truck was stolen for the module.