Why is actuator not kicking in my 1998 Cheverolet Yukon not kicking in when engaged?

check that the 4x4 actuator in the transfer case is engaging
( vacuum lines or electrical solenoid)
check that the auto engage for the front wheels is engaging

check to see if you have automatic hub locking. These units can be vacuum or electric operated and are prone to failure of the system

Pretty normal for some clunking and clanking on electric transfer cases especially if you don't use 4 wheel drive much. Its caused by the all the actuators forcing the gear shift. My 2004 yukon does it as well but works fine when in use. Gets quieter as gears are worn in. Wouldn't worry about it.

If you hear the click in the floorboard then the problem is either the vacuum switch on the top of the transfer case, the vacuum actuator under the battery tray or the cable from the actuator to the front differential lockout. Changing all three will cost less than a hundred bucks if you shop around for the parts. The vacuum switch is the part where the three hose bundle attaches on top of the transfer case. The actuator will pull the cable when engaged, you will feel it pull when you engage the 4wd. It will move slowly. The other thing to check is the vacuum hoses between the source on the back of the motor, the hose from the switch to the actuator and the vent attached to the trans dipstick. If the vent is clogged it won't engage or disengage. Good luck

It's most likely the "four wheel drive actuator" This is located on the front differential housing. It's cylindrical shaped and has a large hex (about
1-1/4") and two wires coming out of it. Usually they short out and blow the fuse but, I've also seen where they just quit working and sometimes they just get slow to work. The "actuator" has a heating element in it and it warms up, some sort gas, causing it to expand thus engaging the front wheels. In cold weather it may take a minute or so for it to engage, so put in four wheel drive and wait for a bit and see what happens.

Normally when I see this it almost always turns out to be the actuator on the front differential has failed. It is possible that a fuse has blown but you may want to confirm that the solenoid is not bad.

your problem sounds like either the transfer case control module located where you hear the clicking sound, or the actuator on the transfer case itself.

try unplugging the transfer case control module and then plug it back in, try engaging 4wd again (make sure your in neutral, coasting at 1-2 mph might help as well) if it still doesn't work check the actuator itself to see if the actuator is trying to engage. if the actuator is trying to engage but doesn't, take the actuator out and check it for wear or damage. if the actuator seems fine and it responds to the buttons when pressed i'd go after the transfer case control module as the culprit. ran into that a few times on those s-10's. 3 out of 4 that i've seen were fixed with a new tccm. 1 of the 4 needed an actuator, check your local junk yard for a working tccm or actuator.

hope this helps!

sounds like the hubs arent locking. try that or there is a modual under your drivers seat or in drivers kick panel could be coulprit

If you remove the actuator and push the collar inside the axle you shouls be able to lock the front end. As a temporary fi we use to cut 3/4 inch of wooden broomstick and place the piece inside then screwed the actuator back in carefully and slowly. If you were stuck in the middle of nowhere and needed 4x4 to get home this wood work. Haha

I just fixed a friend of mines 96 yukon...shift to neutral press 4H and u can hear the actuator make noise (we even replaced it with a new one his idea and the same thing happen as old one), so as he hit the switch for 4H i layed under it (on 4 jack stands) and I could hear the motor on the transfer case make a loud noise (well thats working) and before all this I asked him did u check all your fuses (he said guarnteed to be all good) one night it was bothering me so i looked through the owner manual for the yukon and in the fuse box on driver side by the door there are (2) fuse for the 4wheel drive unit,pull one of the fuses good...pulled the other one and it was blown put in a new fuse and it works like brand new..pull fuse for anything that has to do with 4 wheel drive componants,