Alright, I have an 01 LT with the 4 button 4x4. Auto 4x4, 2 hi, 4 hi, and 4 low. It is currently in Auto 4x4 because of the roads but when I push it to go into 2hi, only the 4lo light flashes and it engages into 4lo. But then I still can't go to 4hi or 2hi, just back to auto. Any ideas? No lights flash on the 2hi or 4hi. Thanks.

Anyone have any ideas?

Nothing that hasn't already been said in numerous other threads. You have the NV236 transfer case which will require a full feature scan tool to diagnose. If it cannot complete a shift, it has likely stored a code which will point you in the right direction. Start there.

I've got a similar problem with a 99 blazer. Stuck in 2wd with Service 4wd light glowing on the dash. I've searched this forum several times using different phrases but all I seem to find is the same above post telling me that what I'm looking for has been posted in numerous other threads. So where should I look, please?

If you would search for "NV236" and add in other phrases, you would find out that the NV236 transfer case requires the use of a Tech2 or equivalent full feature scan tool which can access the TCCM to read the stored codes.

There are some things that you can do yourself. You can remove all of the connectors to the switch, TCCM, and encoder and make sure that corrosion is not causing intermittent connections. Clean all of the connections with electrical parts cleaner and a brush and reassemble with dielectric grease. You can test the resistance values (search for "NV236+resistance") that result when certain buttons are pushed on the switch in the dash. Beyond that, you really need to get the stored codes to further the diagnosis. You could try just replacing parts, but that can get expensive.

The threads are there. I should know, I have written many of them. Keep looking. It gets kind of old to keep repeating things... If I can get some time, I'll actually pull all of the information together, but this time of year... Not gonna happen.

Thanks for the assist!