I have a 2005 Tahoe LT 5.3 with on demand 4wd . I can not get it into any 4wd option. After looking around on the Internet for a while everything I read was pointing to the transfer case actuator. Which I replaced and it did not fix the problem. I do not have a service 4wd message displaying. The best I can explain is when I push the 4wd hi button it tries twice because I can hear two distinct buzzing sounds... Maybe TCCM or sensor module ? Is there a way to test which it might be without a GM specific diagnoses ?
By the way, the lights on the switch do blink when it tries to go into 4wd but they won't stay lit (the 2wd light comes back on)

Any help with this would be GREATLY appreciated !!!!

 

Probably the shift solenoid.

 

I'll see if I can see which one the buzzing is coming from, that should be the culprit (I hope)

Thank you for the input !!!