when I push the button to engage 4wd the lights flash and it goes in fine but they keep flashing till the service light comes on however getting it to come out of 4wd is almost impossible please help I don't know if its the vacuum actuator or or something more serious

 

my 2000 was sticking in 4wd and the service light came on reading an encoder motor code. I unplugged the battery and the encoder box in the passenger kick panel for like 20min and plugged them back in and it fixed the issue.

 

Thank you I will try that

 

Both my 99 Suburban and Blazer have this problem at times. The Suburban always has to be put in reverse before itll go back to 2w. My blazer I always end up trying many times before it works and it never goes into 4hi. Sorry I cant be of more help, I guess I need that same question answered for myself.