my wife got this blazer. We took it out to check 4x4 and it didnt work. When we select 4l i can hear it change under the truck but the lights dont come on the dash when button is pushed. However when i hit the auto the light flashes and stays flashing. The vacume actuator that is located under the battery tray doesnt do anything when any of the buttons are ingaged.im assumeing it a vacuum issue. Ive replaced two of the lines but the one coming from the actuator comes out then goes under the radiator and i lose sight of it. Im very interested in trying resolve this issue my wife bought a lift kit and brand new 31 inch tires but all the be useless without the 4x4 working. Thanks in advance for any help.

 

Do you have vacuum at and going through the switch on the firewall ?. can you apply vacuum to the actuator and make it work ?. Do you hear the TCCM under the passenger kick panel clicking when any of the buttons are pressed ?.....if no clicking check the fuses and the connector on the TCCM ...it commonly corrodes and the result is bad connections or bad TCCM. Can you hear the encoder motor under the vehicle making noise ? ...Is your service 4x4 light on ?...poke around with the search and you will find all the procedures for testing your system and info like voltages and resistances you may need to check ifs its on the electrical side....could even be the dash switch , but some testing will be required....If I find the links I will post them. You said Auto button so you have the 4 button system...correct?.

 

yes i have the four button system.i had my wife hit the button while i was under the truck and the motor on transfercase seems to be working. The tccm clicks also. Ill do a search now to find out how to test the vacuum system.

 

the port at the switch that runs to the front diaphragm , you should feel vacuum when 4x4 is selected...I just see if a small piece of paper gets sucked to the nipple. you can also bypass the vacuum switch by hooking the 2 lines together and see if the front diff locks under the steady vacuum .

 

hey thanks im at my wits end on this thing this whole vacuum system thing stupid there so many things that can cause this issue