ok its a 99 blazer with auto 4x4 than 2hi 4hi 4lo. the light flashes on all them but the 2 wheel.. you can hear something tryin to engauge on the pass side..sometime the 4lo light will stay lit but doesnt work..

 

Sounds like it could be your actuator (on the tcase) or your module up on the dash could be toast. That is a common problem with these blazers.

 

if the lights are on,(the little yellow ones) most likely is the actuator. do you have a service 4wd light on?

 

no the lights not on

 

the service light or the backlight on the 4wd switches

 

On the passenger side is a collar that locks the passenger front axle. This is actuated by a cable which is first actuated by vacuum initiated by the transfer case. If I am thinking correctly, the 4x4 lights (push buttons) on your dash will blink until this is locked into place. If it never locks then they (4x4 button chosen) will blink until a timeout is reached. I am not sure why all of them would blink...

Is vacuum actuator working properly?

 

no the service 4wd light is not on and only the button that is pushed will blink except 2wd that will go back in right away..how would i test the vacuum actuator?

 

i dont know how to test it but when my 4wd wouldnt work and your symptoms are almost word for word as mine. my actuator/motor was at fault. its one piece unit