05 tahoe only drives in 4wheel auto and if put back to 2wd the came on but it won't drive. If u reverse it and than put in 2wd it will only drive for little ways and goesin neutral. When put it in 4hi it make a loud shifting noise and it wo't go in to 4lo. The like just blinks. Service 4 wheel come on .

SOURCE: 93 4x4 auto-tranny. When I

check the hubs the grease gets old and binds up instead of sliding(makes it hard for gears to mesh

SOURCE: Will not shift into 4HI

These have a problem with grounds, i run a ground from my frame to transfer case

SOURCE: s10 pickup 4wheel drive wont shift from 4hi to 2hi

Mine is on the front drivers side, is yours? I just about fell over when I discovered who they designed it!

SOURCE: 2002 Chevy Silverado clunking noice when shift from 2wd to 4hi

It is somewhat Normal Depending on how Loud the Clunking is. This is a Common Complaint on the Chevy 4x4's. I have verified this through the Dealerships here in Oklahoma and they all say the Same thing But, I am with you, They should go into 4x4 without that Clunk for as much as we pay for them.

SOURCE: 4HI and 4LO light flashing 2000 Blazer LT

it is very possible that a wheel speed sensor is open or reading erratic, causing the ECM to override the 4WD switch. Borrow/rent/buy a scanner that will tell you this info,