2000 chevrolet silverado 1500 4wd front differential not locking in

Last night I was trying to climb a paved hill that was icy. I started sliding backwards down the hill and tried to engage my 4hi, my 4hi light blinked 3 times and the light went to the "auto" position. I got down the hill and turned around. I tried to engage the 4 hi again while rolling forward at about 10-15 mph, the transfer case, or something around the transfer case, made a noise that sounded like the edge of a card in a fan. The button said it was in 4hi but the axle was not. I got it home and started looking at it today, I jacked up all 4 wheels and even in 2wd 3 of the wheels will spin and both driveshafts will. When in 4hi all 4 wheel spin when off the ground and in 4 lo all will spin. When I put the truck on the ground only the back 2 wheels spin on the ice and you can tell the 4wd is not engaged even though the light says it is. There is no service 4wd message or light on. It seems the truck cannot get into 4wd while under load.

I have read where the actuator on the transfer case can cause a similar problem, but I was wanting to be sure it could not be anything else before I go out and buy a new one. The transfer case is full of fluid and has been working perfectly with no noises or anything else.

Thanks,

Dalton

Here is a quick test. Get the truck back on the jack stands.
Start the truck and put it into 2WD and Transmission into PARK (you can leave the truck running if you wish).
Have a buddy hold one rear wheel, you the other.
Both of you try to turn your wheel.
One wheel should turn, the other not (PARK in transmission is holding it)

Start the truck, place t-case into 4HI (again, leave it running if you wish)
You and your buddy go to the front wheels,
Both try to turn their wheel,
Again, one should turn and one should not (it is connected to the PARK pawl through the t-case).

If the wheels turn, check the front driveshaft watch for turning.
If front driveshaft is turning, the t-case is not in 4 wheel drive.
If front driveshaft does not turn, you have a problem in the front diff, or with the passenger axle disconnect.

So far this morning I have checked the front drive shaft, which is good, the teeth in the transfer case where the drive shaft goes in is good, I have replaced the t case motor, I have checked the 4wd actuator in the front end it also extends when 4hi is pressed. I am going to try RayVoy's method next to see where that takes me. I am hoping my t case is not ruined.

Ray, does the IGN still have to be ON for the front drive axle actuator to stay engaged?
I seem to remember another post here recently about the font axle disengaging when the truck was turned off.

Ray, does the IGN still have to be ON for the front drive axle actuator to stay engaged?
I seem to remember another post here recently about the font axle disengaging when the truck was turned off.

Scott, if I go by the trucks that I have owned, it does not seem to matter if the key is on, or off. It apears as though the motor stays in place and the clutches stay engaged.

What does seem to work strange, on my trucks, I have backed into my driveway in 4x4 (icy roads and driveway is up hill and covered in ice). I have turned engine off and thought, darn, wanted to be in 2WD in the morning, so I've moved the selector to 2WD (with key off). Next morning after starting I am still in 4HI and it stays there, I need to move selector to 4HI and then back to 2WD to have t-case shift into rear drive.

So, I think it will be ok, turning off the key.

Scott, I believe the post you are referring to was about a mid 90's truck with the old style thermal activated actuator. 04's use an actual electric motor. i never tested it but it makes sense it would stay in place until commanded off.