The trouble I'm having with my '02 f250 is the transfer case will not shift into four wheel drive, and the 4x4 light does not come on although it flashes during the bulb check cycle. I checked the fuses and relays, changed out the switch on the dash with a known good one and took the shift motor off of the transfer case and shifted it manually with a wrench just to make sure it wasn't a problem inside the case. I am down to thinking it is the position sensor on the transfer case shift motor or the GEM. Does not apear to be getting power to the shift motor. I don't have a code reader but am not opposed to paying someone to read codes if that will help. Does anyone know how to check either the GEM or position sensor. Would like to diagnose it further before throwing parts at it. Thanks.

 

The most common cause is the shift motor itself.