I have a 2000 Blazer (s10), 4.3l with the 3-button 4WD button. When I push the 4HI button in Drive, at any speed, nothing happens at all. When it's in Neutral, it will flash the 4HI/4LO lights. It will switch into 4LO properly, but when I try to go to 4HI, it just flashes and returns to 2WD. The 4LO is working, I tried it out in a field.

I was wondering if this would be a vacuum issue, or could it be a problem with the switch/control module?

Any assistance would be greatly appreciated!

 

Check out this thread to check the codes:
OBD2 Non-Automatic Transfer Case Diagnostics by lastcoupe & swartlkk

Let us know what you come up with.

The Tech Article (DIY) section contains a few different posts about the NV233 transfer case that is in your truck.

 

i had the same issue with my '98 last year when i bought it (that's why i got it so cheap). mine has the same t-case as yours, not the "Auto 4WD".

everyone that i talked to (@ GM & my driveline guys) said it was the encoder motor on the t-case. expensive as hell (even when getting it @ cost from the dealer), so i said, "screw it! i'll get a whole parts truck for that price!" i searched for 3 months-during the Winter when you want 4WD the most-found a truck, but by the time i stripped the parts truck, my 4WD started working, and hasn't given me any issues since. the only thing i did was pull apart the dash to replace the factory deck (CD wasn't working), and i think the switch must have been the issue, 'cause it's the only thing i touched related to 4WD in the truck. knock on wood that it'll stay that way, now that Winter is upon us again.

FML, i think i just jinxed myself with that comment! hahahaha

so check your switch, since it's the easiest thing to check (IMO).

 

Actually I think that I might have found it. I was checking the Actuator under that battery, and I sprayed the cable with WD40. I was then looking at the wiring under the vehicle, and discovered that a zip tie had come loose and allowed some wires to rub on the axle. The insulation was gone, so I cleaned them up, and wrapped in electric tape. Whatever I did, it works now!


Thanks for all the help!

 

Good deal!