Well bought a 99 blazer about a year ago. I used the 4 wheel drive once, worked great. This winter got a snow storm tried to use it and it didn't work. It is push button (4 button) has the auto 4x4. This is what happens I push 4hi and it blinks and says service 4 wheel drive but wont go. It will go in to 4lo, but still blinks and says service. When I push 4hi I do here a click in the tccm but nothing happens. I have pulled the battery out and looked at the vaccum actuator looks fine. I have checked the tccm it also looks ok. I pulled out the courtesy lamp fuse and the atc fuse left them out for a few mins replaced them turned the key on and off five times still nothing. Any ideas would be awesome Im lost. Please help thanks.

 

The 'service 4wd' light is very much like the check engine light. When it turns on, the TCCM has stored a trouble code indicating the problem. You need to get the TCCM scanned to retrieve the trouble code. This can only be done by a scan tool capable of communicating with all of the serial devices in the truck (GM Tech2 or equivalent full feature scan tool) and is typically something that a shop must do (autozone, etc scanners are usually not capable of this). Get the code and let us know what it is. We'll go from there.

 

Thanks I will get it scanned asap and let you know. Question though the service 4 wheel drive light only comes on when a button is pressed, so is it possible that it might just be a vaccum line is off or broken. I have noticed that some other hoses where looking kind of rough.

 

You can look over the lines relatively easily. You will have a line that runs from the engine to the solenoid on the firewall and then one that runs from the solenoid to the actuator under the battery.

 

I found a hose off. Here is a link to a photo that is identical to my issue could this be my problem, and if so where does it go/location? http://www.kylestubbins.com/files/images/IMAG0025.JPG

 

Goes into the vacuum reservoir which is located inside the driver side fender right in that general area.