I think it is great that he took it in to a PROFESSIONAL. I work at a repair shop and it has been my experience that it could be any of the following things:
Control/GEM Module (yes, the 4X4 system has its own computer)
The switch on the dash (push button, or twist knob-if so equipped)
The encoder motor (or switching motor) on the T-case
Problem inside the T-case (they have clutches, chain, sprocket, gears, bearings, shift fork-all kinds of neat stuff in there)
Faulty hubs (IF your truck even has hubs-some new trucks DO NOT)
Wiring or Fuse problem (least likely, but still possible-easiest to check)

The bottom line is it needs to go into someone who knows how to test these different things to come up with an accurate diagnosis. There is no other way. Working at a shop, the one thing that really bothers me is when people come in and tell me what parts their vehicle needs. That sucks because 99.9% of the time they are wrong, and then I have to [censored]-foot around trying not to make it obvious that they are WRONG, and trying not to hurt their feelings.

My advise, take it for what you will, when you take your car/truck to a repair shop-DO NOT arm-chair quarter-back diagnose the problem. Simply stick to telling the person at the shop the PROBLEMS that you are experiencing. You are coming to us because you trust that we know how to figure out what is wrong with your car-don't short circuit that relationship by TELLING us what parts to replace! You wouldn't go to your doctor and tell him-"I have pneumonia and I need you to write me a script for pennicillin". Your Dr. would laugh at you. You see how crazy that is? If you really knew what parts your car needed-why did you bother to come down to our shop?

On the other hand, I LOVE those customers that come in and can accurately describe the exact circumstances in which the problem occurs, and then they do something really cool... They wait to see what we think the problem is without offering their own suggestions as to which parts the car needs. Does not happen often, but oh, when it does, it makes the whole day go easier.

Don't be the "my car needs this part" guy.. PLEASE? Let the pro's check it out, and then tell you what it needs. That is what you pay us for.

Quackattack-I'm glad you took the truck in. Hopefully you didn't go in and regurgitate any of the information in this post on the poor guy at the shop. Let us know what it turns out to be as I'm sure others will want to know as well.

I'm not intending to hijack this thread, but do you guys know a good off road shop in Dallas? I want to get a locker installed and I have alot of questions, like I always do. Thanks

Andy, I do all of the differential work for the shop here. You can PM me with any question you like & I can help you to the best of my ability. I'm in Houston so the proximity is not great but at least I can guide you from a distance.

I can help tremendously if it is a Ford.... only thing I've worked on for over 18yrs. I can help ya w/ basic questions and answers on the set-up of a diff if that's what your questions are about.

Sounds like if the transfer case is working and the actuator is also then whatever locks the wheels to the axles/ cv's is the problem.

Most Fords nowadays use a vacuum hub, but I know some Chevy's are direct splined to the front axles and they turn all the time. The transfer case is the only thing that is actuated to enguage the 4x4.

It's not necessary to lock/ use the 4x4 on a regualr basis. If something is going to stick bind it is the lack of maintenance. I can't think of the last time I locked my truck into 4x4. I'll guarantee ya that it will enguage.

Hope ya get it fixed w/ little out of pocket.