the above noted truck does not change from 2WD to 4WD - the switch works and the transfer case motor works - did find some helpful information to check on another email from someone else but have been told it is the GEM and trying to find one is there something else we can do before changing the GEM would you please send a picture of the GEM so I know what I am ordering and where it is situated to change it - I hope this makes sense
Thank you

 

Better do as much diagnostics as possible to determine if the GEM is the problem.
They are expensive and require programming to your truck's original build, by a dealer.
The whole operation needs to be checked out.
If the transfer case motor runs to it's first position, thats fine but there is a circuit board that has wiper contacts to feed back signals to the GEM and forward to the vacuum control for the front actuator.
If the motor runs both ways per the switch control , is the tranfer case driveing shaft into the transmission working?
These are the items to know before buying a module and haveing the programming done and find it did not solve the problem.
The GEM is located as a attachment to the fuse block under the dash.
Also look at the possibility of a windsheild leak onto the GEM and any fuse issues related to the 4x4 operation.
Good luck to you.

 

There may be a range sensor on the front of the transfer case, my '99 has one. It's about the size of a temp. sensor hex, and has a two wire harness. If this is shot the transfer from 2 wheel to 4 wheel won't happen. To check, remove the harness, remove the sensor, check the ball bearing in the end, it should be spring loaded. If the ***** rattles loosely, or is stuck up in the bore of the sensor, it's bad. I think they are around $35.00 at the dealer.

Also check the front side of the front differential. If there is a plastic shroud about right in the center, remove the shroud ( 3 bolts), with the truck running, have someone look at the vac linkage while the truck is shifted from 2W to 4W.. If it doesn't work, check the vac from the firewall mounted relay to this vac assembly. If the vac is working when the trans is shifted from 2W to 4W, the diaphragm is probably bad. If you have -0- vac at this diaphragm when shifting, check the relays (2) on the firewall ( passenger side by the starter relay). Check them for bat. voltage with the key on, and function when shifting. If everything so far is cool, check for vac to both relays. Those plastic lines bend all over, and can crack easily.

Dave