I borrowed my friends 95 S-Blazer with the push button 4WD Saturday to go pick up another vehicle about 340 miles away and when I got home the 4WD wouldn't engage. I put it into 4 high once for about 40' after stopping on the side of the road and realizing I was on soft ground. After I got back onto the road I switched back into 2WD and everything seemed to work fine. A few miles from home the road started to get slick so I tried to re-engage 4 high and nothing. Today I checked the fuse and it was good, when the truck starts the 4 high and low lights blink on for a second but 4WD still doesn't work.
It's still under her used car warranty so she's not upset but I'm just wondering if it's anything I did. I feel bad 'cause it happened when I had it and she REALLY helped me out of a bind by loaning it to me.

Any help would be GREATLY appreciated!

How "used" is it? What year? How many miles?

It has push button 4wd, so it could be any number of things. One thing that a few people have problems with is colder weather. The actuator on the axle is filled with liquid, and when the liquid heats up it trips the thingamajig to engage the axle. If that actuator doesn't heat up, it won't engage, and the lights flash to warn you.

This is just one possibility. I may be wrong. It could be any one of a few things. Doesn't sound like anything you did.

It has 90k on it but it's in very good condition. She only uses 4WD when the roads are slick and she's never even had it in 4 low or off pavement as far as I know.
Something I found out at another BBS is that the 2WD light should come on when it's not in 4WD and her's never has since she bought it last April. Also she just got a recall notice for the 4WD ABS so I'm wondering if that has something to do with it.

The main thing I was concerned with was is this something I did and I've come to the conclusion that no it's not. I think it's an electrical problem that has gotten progressively worse and it just so happened to fail while I had it.
Good thing she still has two months and 2000 miles left on her GMAC warranty!:D

check to see if the shift motor on the transfer case is getting power... that seems to be one of the problems with the np233's

Encoder motors... no fun

Just to let you know, she got it fixed today and it ended up being the shift motor ($500) and the dash switch ($50).
Neither were covered under her GMAC warr. but I can't believe they don't consider the shift motor a driveline item.