ok i got a 2001 GMC jimmy automatic with a 4 button 4wd switch. i had the problem where only 2hi will work and all others just blink. i replace the switch under the battery after that didnt work i bought the transfer case switch for 15.00.
when i was looking for the t-case switch i found a vacuum line going to the t case that somehow made its way onto my exhaust pipe and melted a hole. i repaired the hose but its still not working.
and where does this t case switch go? i got a switch that has 3 vacuum lines goin into it is this the right one? i also freed up the cable that goes to the front axle. i have read a lot of these 4x4 problem posts but i have yet to find a pic of this switch.

 

Your problem sounds quite normal actually. You just have to search for the threads that apply to your transfer case (NV236). With that said, I doubt your problem is with the vacuum system. I would inspect the switch (testing the resistance values) and also inspect the connection at the TCCM (passenger side kick panel) and on the encoder motor (at the transfer case) for corrosion.

On the 4-button (NV236) transfer case, there is no vacuum switch on the t-case itself. The vacuum supply to the front axle is done via the electronic solenoid valve located on the firewall.

 

i have 4x4 problem. 2000 s10 pick-up the truck has been stuck in 4 wheel hi for 6 months, its bad enough where it howls now going down the road. i think the front diff is junk now. but tryed to replace encoder today and the shaft is like 20 degrees off from lining up with encoder. couldnt move shaft any more, got it on by lining shaft up and prying gently until bolt holes lined up, then plugged in and tryed it, and did nothing. must i reset computer???

 

just wanted to throw the update out there i know the t case switch is a very likly problem with 4wd on these but it was actully a vaccum line that rotted off an actuator right under the pass side wiper now i have 4wd again


edit** and now i see thats what you told me haha thank you for your knowlege Swartlkk