4wd not engaging

Yes… another 4wd help thread. Having some weird issues with my 4wd not engaging. When switching to 4Hi, I get the flashing 4Hi/4Lo lights. Have to either restart truck a few times or go down and jiggle the tc actuator a little bit to get back to 2Hi where it likes it. I did the continuity test and the results showed DL1, DL2, and ADD with incorrect voltages.

In 4H:
DL1: expected 12v actual 0v
DL2: expected 0v actual 12v
ADD: expected 0v actual 12v

but here’s the kicker. If I turn the tc actuator manually, reassemble it, then flick over to 4Hi before turning the truck on, turn truck on: it’s in 4Hi no problem. Verified it is actually in 4wd as well. So that leads me to assume maybe the ADD is functional after all? And maybe it’s my TC actuator that’s bust?

another side note… anyone hear beeping coming from their ADD when attempting to switch to 4Hi? Almost like a motor trying to turn kind of beeping. Check out the video.
https://youtube.com/shorts/WSgCYeCFUrs?si=8wfMbvKeThJryQS-

 

It's as if the nothing changes at all in 4WD. (at least with the limited info given)
I'd like to see what the LO voltage is in 2WD and 4WD.

 

Are all of the other limit switch voltages correct?

The motor "beeping" is certainly interesting, I haven't seen that before. Do you hear the 4wd ECU clicking at the same time the motor is doing that?

 

All the other readings appeared normal. Don’t have the exact numbers because my multimeter is a POS. If I get a better one I can get it exact.

Yeah the beeping is super weird. Nothing else was making noise besides the ADD. Sounded like it was trying to turn but wasn’t able to. But then all the sudden it did and I got into 4Hi once, after manually turning the tc actuator.

 

It's interesting that you say everything else was correct but you say you had to manually move the Transfer Case Actuator, for TL1, TL2, TL3, and 4WD to be correct the Transfer Case Actuator would have to be in the 4wd position.

The ADD Actuator won't move to the Locked position until the Transfer Case Actuator has shifted to 4wd and the Transfer Case has engaged 4wd.

 

I recently replaced my ADD actuator — it worked, but very slowly, and inconsistently. Perform your tests a few times just to make sure they are consistently repeatable.

If I am reading what you wrote correctly, the ADD works fine if you manually move the TC actuator? Is that not your answer right there?

I would start by replacing or repairing your TC actuator and see where that leaves your ADD actuator. You may have an aging ADD actuator, but it sounds like (also) you have a nonfunctioning TC actuator.

Edit: actually, maybe first test your position sensors on the TC and make sure they are behaving normally before you undertake any big expense.