4HI light blinking and 4WD is not engaging

I have a 2007 5.7L Crewmax that is bone stock, 174K miles and hardly any offroad use. When I select 4HI from the dash switch the 4HI light in my instrument cluster will start flashing slowly for about 6 seconds. After 6 seconds it flashes quickly. I have confirmed the transfer case drive shaft engages during the first 6 seconds and disengages after 6 seconds. The front wheels never engage. The fault code states that communication with the ADD actuator has been lost. The ADD is the actuator on the front differential. The dealer has tried the following:

1. Installed new OEM ADD actuator and verified it should work
2. Swapped 4WD ECU from my truck with another that came from a functioning truck

I have done the following -
1. Verified continuity of all wires from ADD electrical harness to 4WD ecu electrical harness.
2. Verified continuity of all wires from the transfer case actuators (4HI and 4LO) to the ecu electrical harness.
3. Took apart transfer case actuators and verified both electric motors work. Also cleaned all contact points and verified there is no corrosion. Both look brand new.
4. Disconnected the battery and ECU electrical harnesses over night

None of the above has solved my problem. The dealer wants to install a new transfer case actuator since the 4wd ECU and ADD have been ruled out. They also feel like the dash switch is functioning properly. But I am not convinced the transfer case actuator is the problem given that it tries to do its job and has continuity with the 4wd ECU. Its about $4K to install a new transfer case actuator since the transfer case needs to be removed and split open. Are there any other troubleshooting options I can try? I do not want to spend $4K and find out the problem has not been fixed. Thanks!

 

That's too bad. Hopefully you can do some reading and see if anything pops out to you.
https://www.tundras.com/threads/2007-2020-transfer-case-actuator.61182/


https://www.tundras.com/threads/g2-4wd-actuator.47592/#post-1268229

 

You have confirmed that the transfer case actuator is working, why replace it? Dealer techs are generally lazy and would rather you buy a bunch of parts to install instead of doing real diagnostic work. If you throw enough parts at a problem, it usually goes away without having to think. If it were me, i would pull the add actuator and with it in your hand still connected go to 4hi. You are looking to see if the front driveshaft still engages and that the arm of the actuator moves. If the arm moves and the flashing light goes solid, you have a mechanical issue in the diff or the tech installed the actuator incorrectly. If the add arm doesn’t move or moves but still get flashing light, you have an issue with the add actuator, the t case actuator (less likely)the wiring or the ecu.

 

FIXED!!!!

Thanks to the https://www.tundras.com/threads/2007-2020-transfer-case-actuator.61182/ thread I discovered I clocked both my 4HI and 4LO transfer case actuators wrong when I reassembled them. I reset them according to post #76 for 4HI and post #159 for 4LO and voila, I have functional 4WD again!

I think what happened is my ADD shat the bed but I went into the transfer case actuator as my first root cause. I unknowingly re-assembled it wrong and then went after the ADD. The ADD was definitely crapped up but replacing the original ADD with a new ADD fixed nothing because I buggered up the transfer case actuator timing. The dealer was also stumped and wanted to charge +$4K for a new actuator which technically would have fixed the problem but my original actuator was never bad. It was clocked wrong by me after following advice from several you-tube videos that gave bad instructions. Thanks to V@pors and Oochi20 for setting me straight.

 

@Frenchtom Awesome!