Here goes,

2004 Blazer, 4WD 48,000 miles

I live in MASS and we got 10 inches of snow yesterday with some freezing temps and some driving winds. I was out driving around noon and the 4WD worked fine. I get back into the car around 6 and the 4wd no longer works.

The 2HI button lights up, the 4Hi does nothing, the 4Lo lights up and reverts back to off when I do nothing.

The vehicle idles fine so I am not leaning towards a vacuum leak.

I checked all the needed fuses and they looked fine, I've seen people mention disconnecting the battery and reseting the memory.

Anyone have any thoughts on what is really going on here?

 

If you do not have an Auto4wd option, then you can run through the diagnostic steps found in the DIY article - OBD2 Non-Automatic Transfer Case Diagnostics

Other things to look at would be the connection at the back of the switch, the connection at the TCCM (transfer case control module) located behind the passenger side kick panel, and the connection at the encoder motor on the transfer case.