99 Tahoe 4wd not engaging.....however.

[res02p35]

Hi guys, I'm back after getting my 99 Tahoe running again.
Strange thing I can't determine. The front driveshaft turns, so the encoder motor on the transfer case is working. When I select any 4wd mode I hear the front actuator engage. I even removed it to verify operation. It is indeed engaging but still the front wheels are not turning. Could the tccm be the ussue here?

 

[Fless]

Moved you here from the 2021+ section

 

[B-train]

Check the engagement pin on the front axle. They have an electronic actuator that engages the front dif. Spring loaded return to open. It should have a 2 pin harness and be on the passenger side of the dif by the axle tube.

 

[res02p35]

I thought that was the actuator which is working as I removed it and pressed the 4wd button. It popped out so it is engaging.
I do see this harness on top which must be what you are referring to. Its on top of the actuator.
It is not connected to anything? I do see another 2 pin connector there as well but they don't connect.
Looks like something may be missing there(maybe a module)
I will research this a bit more.

 

[Fless]

Pics would help us see what you're seeing.

 

[res02p35]

 

[res02p35]

So there are the 2 wire connectors, if you look there is a bracket which I assume something should go there. The white connector goes above the actuator. The red connector comes out of the crankshaft position sensor harness.
I thought the white connector was a propshaft speed sensor, but B-train said that would be a pin to engage the 4wd?

 

[res02p35]

Not sure if something is missing as the PO has all the abs and O2 sensors unplugged.

 

[Eman85]

If you jack the truck up and engage 4wd the frt. actuator should lock in the rt. axle. You should then be able to turn the wheel by hand and feel the axle being engaged to the rest of the frt. differential. If you jack all 4 off of the ground and put it in 4wd with the truck running and in gear does the frt. driveshaft turn? If it does but the frt. wheels don't something is wrong in the actuator section. If memory serves me there is a switch to show engagement on the ones that have the lever engagement and the diagram that lights up. That might be what the harness was for.

 

[res02p35]

Yes the front driveshaft turns when 4wd is engaged.

I took it off the stands, put it in 4wd, drove it then jacked up the front.
The wheels and shaft turn by hand, but they are not turning together. Something in the diff must not be engaging.
Not sure how the stub shafts get engaged.