4x4 won't go to 4hi
 

when i press 4hi, 4hi button lights up as if there were no problems, but it engages in 4lo instead.i can go back to 2hi from there but i have no 4hi. so i'm assuming the vacuum to engage 4x4 works and whatever switches it from 4lo to 4hi is the culprit.

RE: 4x4 won't go to 4hi
 

Do you have Auto4wd? If not, check out the thread in the DIY section. OBD2 Non-Automatic Transfer Case Diagnostics