I have a problem with my Blazer I put it in 4whl. drive last week, I should have not done it because my service 4x4 light has been on for awhile. I tried to put it back in 2whl. drive high the light flashes and I can hear the tccm clicking and the shift control motor energizing, then it goes back into 4whl. drive high. I have already replaced the transfer case control module (not cheap) did not fix. I also have replaced the 4 button shift selector on the dash, still no fix same problem. I pulled my batt.and tray out today to look at the shift control aucuator and the diafram is sucked in even with the vacuum hose disconnected. Ive run out of things to check can anyone help? Thanks

 

try driving in reverse while changing to 2hi .
you also might be able to push the cable by hand into 2hi . ill bet it is either the cable or the actuator .