I've got a '99 ZR2 Blazer with about 125,00 miles on it. Never had any issues with the 4WD until recently. It's got he push button on the dash with the automatic 4WD option. I tried 4HI the light just blinks and won't engage. Same with the auto 4WD and 4LO. I can hear the control module click when I put it back in 2WD so I'm assuming it's working. I've heard there have been some issues with the GM Push Button 4Wheel Drive but this is the first problem I've had and I don't really know how they work. My Haynes service manual hasn't been any help at all. Can anybody tell me where to start troubleshooting and what to look for? Thanks a ton.

 

Well, I see nobody responded but we found the problem anyway. Just incase anyone runs into the same issue, I'll tell you what we found. There's a vacuum line under the battery box that goes to some sort of actuator or something. Anyway, it had broken so we cut off the bad end and slid it back onto the fitting and it's good as new. I hope this info is usefull to someone.