My 01 zr2 blazer won't engage into 4hi 4lo or auto 4wd...when you press the buttons the lights just flash. When you hit 4lo you can feel it engage underneath the truck but the front wheels never spin and the light just flashes..I put in a new tccm and 4x4 selector a year ago..there is no service 4wd light on my dash either...last time I took it off road it worked fine...any suggestions

 

Truly a pain in the neck but you have to see if the vac actuator is working, it's under the battery pan.
You need to take the battery out, un-bolt the pan, put the battery back and start the truck. Now with the truck running take the battery out, put it on the side of the truck and with a set of jumper cables connect the battery back to the truck cables. This is so I have been told, not to fry the alternator by running it with the battery not connected. Take the pan out. What you have now is a running truck connected to your battery and a clear view of the actuator.
Push your button and see if the diaphragm engages.

 

Trying this right now ill let you know what I find

 

I did what you said and found the actuator was just laying there. The bolts had come out somewhere along its life. I took a closer look and found the vacuum hoses in rough shape so I replaced them and now it works!

Thanks!