I have a 2003 Excursion 7.3 Dieselthat has a 4wd high/ Low/ off switch on the dash with the locking/auto hubs. The 4wd does nothing when I switch to 4high or low. The switch and the electric motor on the front transfer case have both been replaced and still nothing. I can manually lay under the truck and turn the shaft on the front transfer case and feel it engage into different gears so I think its something electrical. Its at a dealer now who is telling me that there is a problem with the GEM module. They have replaced the GEM and "are still working on it". Does the GEM control if the 4wd will go in or not? Any help or suggestions would be appreciated.

 

The system is ESOF (Electronic Shift on the fly), or Electronic shift control.. Functions are controlled 'in part' by the Four-wheel control module....

 

Could possibly be a vacuum supply issue to the hubs. Have seen this numerous times.