Another 4wd 4x4 engagement problem. Actuator always goes to center position.

@N84434 and @BubbaW , I found PHM's post on tundrasolutions recommending you two as the 4wd system gurus, so I am here to ask for help.

The 4wd has not worked since I have had my 2001 Sequoia. My dad had the truck before me (he bought with 60k miles, I took over at 386k, now has 430k), but he does not remember much about when it started to act up. I believe his mechanic had attempted to diagnose it at some point before I got it, but I do not know what was done.

Using this video, I have determined that both the ADD and transfer case actuators are working properly. I can engage or disengage either actuator by applying power directly to the terminals. I have inspected each and found them to be clean and corrosion-free.

I tested the two transfer case position switches for continuity. One seemed to have some dead spots so I replaced it. After mistakenly acquiring a switch that was a resistor that varied with the position of the plunger, I have acquired what I believe is the correct switch, 84222-12010. It is tested to provide continuity. I have tested that the two switches provide continuity when they are installed and the transfer case shift rod is in the center (4hi) position.

Unfortunately I do not have a manual for a Sequoia, only a 2003 Tundra. The maker of the video listed above is using a manual for a 2003 Sequoia, which confirms that the three positions of the transfer case shift rod correspond to different functions on the Tundra and the Sequoia.

On the Tundra, as far as I can tell from the 2003 manual I have (pp. TR-44 and TR45):

Rod Out = 4 Lo
Middle = 4 Hi
In = 2 Hi

Since the Sequoia has a manual lever to select between Hi, Neutral, and Lo, the three positions correspond to different functions: 2 Hi, 4 Hi, and 4 Locked (not 4 Lo), where the front and rear axles are locked together as opposed to connected by the Torsen differential. Positions as follows:

Out = 2 Hi
Middle = 4 Locked
In = 4 Hi

I have confirmed this by comparing a screenshot of the manual used in the video with the wiring diagram from the 2003 Tundra I have.

Here is what happens when I put the system together:

I make sure that the shift rod is all the way out (2wd. Front output shaft spins free. The ADD is also confirmed to spin free. I install the gear into the transfer case actuator such that the contacts are at the corresponding point in the rotary switch's travel (all the way out). I connect all the wiring connectors.

When I turn the key to on, I hear a click from the transfer case, and the orange center light in the 4wd indicator array (4 green lights for wheels, one orange light for transfer case) starts flashing. I can press the 4wd button and it will turn the green wheel lights on and off, but nothing else changes. When I check under the car, I find that the transfer case actuator has indeed shifted the transfer case into 4 Locked (center rod position).

If I turn the vehicle on with the transfer case in 2 Hi, it will shift into 4 Locked. If I turn the vehicle on with the transfer case in 4 Hi, it will shift back to 4 Locked as well. If I turn the vehicle on with the transfer case in 4 Locked, it will do nothing. Sometimes it will shift into 4 Locked with no input. Sometimes it will wait until I touch the 4wd button. Regardless, once it is in 4 Locked, it makes no further attempt to shift. (In each of these instances, I have tried disconnecting the battery, making sure the transfer case, ADD, and manual shift levers "agree" with each other, and reconnecting the battery. No change.) After the initial shift, if I push the 4wd button, the green wheel lights will either light up or turn off, but the orange transfer case light stays flashing, and there is no response from the shifting system.

Why does the actuator want so badly to be in the center, 4 Locked position???

One theory I have entertained: the low-range position switch faulty or stuck, telling the 4wd ECU that the transfer case is in low range, and thus it always shifts the transfer case into 4 Locked to try to compensate. But the transfer case does not need to be in 4 Locked in order to be in low range (the opposite is, however, true). Also discounting this theory is the fact that the ADD does not correspondingly lock when the transfer case shifts into 4 Locked from 2 Hi.

Maybe you will say test all connections for continuity at the 4wd computer. I have not done this yet and realize I need to. Before I go through that tedious process, though, I wanted to post here and see if what I am experiencing calls to mind an obvious point to check that I have overlooked.

If it helps, my VSC, ABS, and Brake lights are all on. I have an explanation for the ABS light being on--I took out the fuse because I was having random wheel lockups at speed and didn't care about ABS enough to figure out the problem at that moment. The 4wd problem predates pulling the ABS fuse.

Also, if anyone has a link to a Repair Manual for my specific vehicle, that would be great. If someone can provide a good wiring diagram for my specific system, I'd be most grateful. I don't mind doing the checks if I know I'm not guessing about slight variations based on year and model. Hopefully with your help I can save the factory system. Otherwise I'm going to throw in the towel and convert to an all manual J-shift case and Dana solid axles.

Thanks,

Luke

 

I’ll mull over what all you have written and try my best to understand but until then the wiring diagram for 01 Sequoia can be had here at Tundras….

https://www.tundras.com/threads/ultimate-sequoia-wiring-diagrams-collection.111234/

 

Someone reposted a killer video showing how to pull apart the actuator and repair it.

 

Welcome Rusty;
I don't have any experience with the Sequoia system, but the manual lever seems like it would be very straight forward. I wish we had those in the Tundra. Are we sure the ABS problems aren't contributing to the 4WD system not working correctly? I had a WSS failure last year, but it didn't have an effect on the ability to select 4WD.
The actuators are original to the truck, or have they been replaced at some point?

Have you gotten the truck completely off the ground to allow the wheels to spin, and then run through the selection process?

We'll figure it out...

 

That may have been me...

https://www.tundras.com/threads/intermittent-4-wheel-drive-light-blinking.107641/#post-2771991

 

Thanks for the link @BubbaW. I will try to see if I can gain any more understanding from it and make a serious plan for electrical testing.

I have done all of my testing with the wheels on the ground. I do, however, have the front driveshaft uninstalled until I can get this fixed, both so it doesn't spin when I am driving around with the transfer case in 4 Locked and so it is easy to tell if the transfer case output and the ADD are locked or free. What benefit should I expect from attempting to cycle it with the wheels in the air?

I'm not sure that the ABS and VSC issues are not affecting the 4wd. Is there any way we can find out whether that could be part of the problem? I suppose I could diagnose and repair those issues and then come back to the 4wd. I don't want a 4wd system that is dependent on VSC and ABS, but I also want to figure out what the heck is wrong with this thing. I must say, shifting into 4 Locked seems like a bizarre response to a VSC or ABS fault....

I believe these actuators are original.

 

Ah, yes, I have seen that video @w666, thanks for reposting it. If I had a scope I would definitely recreate that test, with the change that I would do the test at the 4wd ECU connector so as to include the factory wires and connectors. It does seem possible that the computer is getting a noisy signal from the actuator, and thus refuses to move past 4 Locked. I have disassembled and reassembled the actuator countless times at this point, so I am familiar with that part of the process. No evidence of corrosion like what was found in that video.

 

I guess you're almost there with the front driveshaft removed. When I was rebuilding my system, I got the truck off the ground so I could easily run it in gear and watch what everything did real time. It just made it easier for me. Plus crawling under the truck was a breeze with it off the ground. Not that it's difficult to get under there anyway.