I have a 99 blazer and the 4x4 has never worked properly. Now when u hit 4 hi nothing happens its as if the button is broke but ive tried a new button in it. When you hit 4lo while in "N" you can hear it engage and it defenitly is engaging bc i can feel the torque change. I could drive for ever in 4lo and have no probs just limited to very slow speeds. Then once i want it out of 4lo and hit the 2hi button you can hear it disenage and the 2hi light comes on but...its now in 4hi. It will stay engaged for different amounts of time until it clucks and switches back into 2hi. If ya have any ideas whats going on please let me know.

 

Try penetrating oil on the cable at the axle to the actuator mine rusted ffrom not being used and was only going in partially

 

would this be the cable that is coming from the actuato under the battery?