Ok so about 3 months ago my truck started saying service 4wd and I haven't got around to fixing it.. The only lights on the switch that light up are the auto 4wd and 2wd high back lights thetrs no orange lights showing. I don't know where to start will a diagnostic computer give me the error codes as to which component to replace and is there any simpler ways to trouble shoot this problem!? Any help is appreciated

 

Possible bad grounds, one under drivers door on frame looking forward. Another is up under left front headlight on frame along with engine grounds. Possible bad encoder motor and or T/C module. To get codes you need to go to a dealer or a shop that has the Tech2 scanner. Good Luck.