99 gmc sierra k2500 4wd problems

[cbuss]

Just bought the truck got a great deal on it but the 4wd doesnt work. The switches on the left light up and its always in 4 auto but whenever i try to switch it it just flashes and clicks then none of the lights are on? Is it the switch itself or something more serious like the transfer case? 4wd doesnt work even though it says its in 4 auto

[gmtech4]

You have to scan it first and have the code diagnosed , sorry

[00Silverado4x4]

Agreed, must be scanned or else you will be guessing and throwing parts at it. Also how do you know the transfer case isn't working in Auto 4wd? I just ask because until your rear wheels are spinning at a different speed from the front wheels the truck will be essentially "in 2wd".