I am struggling to figure this out. As with other people my 2003 f250 7.3 diesel won't go into 4x4 high or low. The lights come on on the dash briefly when started but no response at all using the switch.I have tried a different switch from another working 4x4. I have tried a different GEM module with the exact part number. No change. All fuses have been checked and are good. The relays are clean and have continuity through their connectors. The input and output side of the relays have been checked and are working properly. I have swapped their positions also. I have popped off the relay covers and can work the relays by hand with the key turned on and I am able to energize the transfer case motor and it will lock into 4x4 high and low and the dash indicater lights come on and go off correctly and the motor is definitely working. Also its not a vacuum issue as some others have had . When you manually operate the relay and the motor locks the transfer case into 4 wheel drive the vacuum pump comes on also.So I am assuming the output side of the relays is working but what ever controls the input side of the relays is not energizing them.There is a constant 12 volts to each relay. You can disconnect the plugs to the gem module and various things quit working so I am assuming its doing its job especially after trying a different one. I have searched a bunch and can't figure it out and was hoping somebody could tell what to do next. It was all working a month or so ago and I went to use the 4x4 and it just would not work.

 

 

 

I just had to replace the vacuum solenoid on my 2011. It just quit working on a camping trip. I pulled my toyhauler onto the beach in 4X4 and it worked fine, when I went to leave it didn't so I had to lock the hubs manually.

 

Guys thanks for the replies but please reread the original post. The vacuum is working. The relays aren't getting energized.

 

Where is the GEM module located that you swapped? Starting in 2002 Ford switched to a VSM behind the radio (GEM was behind the fuse panel up until 2001). From what I understand any time you put in a new VSM it has to be programmed to your truck by a dealership.

From what I read it looks like you've narrowed it down to the relay inputs and the relays themselves (they don't electrically operate). The only other piece is inter-connecting wiring where something may be loose, chafed, or broken.

I have only had vacuum issues with my ESOF so the electrical side is outside my wheelhouse, but if you're looking for some wiring diagrams here's a link to a fee database of them: BBB Industries- Premium Alternators, Starters, Power Steering Products | TSB's & Wiring Diagrams

 

The Gem module that I swapped out was behind and in the upper part of the glove box.Whats a VSM?

 

Behind the glove box is the 4wd control module. I get it now.

The truck (up through 2001) had a General Electric Module (GEM). This controls non-engine functions like window/radio delay, FOB functions (locks/panic), etc. It was mounted behind the fuse panel under the dash. In 2002 there was a major electrical change and it became the Vehicle Security Module (VSM) and the mounting position was moved to under the dash behind the radio.

When you said GEM I assumed the GEM module (which you don't have since you have an '03) and not the 4wd control module and realized my mistake when you said glove box.

My bad.

 

Anybody have amy ideas?

 

It's a very unique issue and it looks like you've narrowed it down. Without being there I still think it's the relays, the inputs to the relays, or interconnecting wiring from everything you've described.

You said you've "manually" operated the relays and things work. Short of jiggling some wires/connectors and cleaning your connections, it looks like it's time for some continuity/signal chasing.

To make things go quicker you can do some half-splitting. Figure out a known good and a known bad from the wiring diagrams and then try to find somewhere in the middle to test. If it's good then go half way between there and the bad, and so on. If it's bad then go half way upstream to the good and test there. This will be the quickest way to find your issue short of taking it to someone who will do this for $150/hr.

Just my .02

 

 

It's sure sounding like a bad ground someplace. Anybody done any other work that took stuff loose, even to then replace that part? If they left a common ground off, it could do what you're experiencing.