Driving to NJ last night and the message centr is showing Service 4WD. System still changes to 4wd-auto and 4wd high ( didn't try the 4wd low ). Does anyone know if you can scan that for a code as to why it was being displayed? Message wasn't dispalyed again when I started the truck this morning?

BTW, 2005 chevy silverado, 5.3L, push button tranfer case, 71K miles. And before Nick says anything, I'm 99% sure that IT'S NOT THE OPTI!

The code will be cleared when you shut the truck off... It has to be read with the engine still on..

Anyway, I've been reading a lot about this recently.. Cheapest thing to do is remove the connectors ont he t-case, clean 'em, and put dilectric great on them. Also, clean the ground wires for the transfer case on the frame.. (On the Avalanche, they're near a body mount, there's a grouping of like 3 of them)

Other than that, it seems to be the switch ($55), but more often, the encoder/motor ($500)

Thanks, I'll check them out.

It's all HOWARDS FAULT!