I have just purchased 2003 Expedition EB with 80K miles on it.
Advance trac service light is on and four wheel drive is disabled.Four wheel **** is not doing anything.Truck runs and drives excellent but without four wheel here in NY is kind of useless in winter. I scanned it and the only Dtc is U1900 no communication.My mechanic friend told me that most likely abs module is shot.
All the wheel sensors are good and no blown fuses.If I change the abs module does it require programming the new module.
What else could be causing this code? I will appreciate any help before I start dumping money into it.

 

Check fuses 11, 15, 16, 20, 103, 112, & 115 to make sure they're good.