4x4 issue

I got my truck about 3 weeks ago. The 4x4 worked fine when I got it, and I've tested it a few times since then and it yielded no issue. But for the past few days, I've had trouble with it.

First, for reference, my truck is a a 2004 V6 TRD with push button 4x4 (and ADD up front).

So it initially seemed it would not engage 4wd. I press the button and nothing happens. No sound from the actuators/transfer case and no indicator on the dash. I checked the fuse, and it was good but I replaced it anyway to make sure. Cleaned battery terminals to rule that. Still nothing.

Today, I decided to do some more testing. And what I've learned is that it appears to actually be stuck in 4wd and will not disengage. The truck seems to have no issue going into 4lo. I can clearly feel a difference right away. Also, the rear locker works (which is what made me think it might be stuck in 4wd). Not sure if the front part of the drive train should move when in 4wd, but it currently is moving.

As for the dash indication, I can't say exactly what the deal is with that. The first time I noticed an issue, it was lit up when I started the truck. And that has happened 2 or 3 more times. When it does, it won't go off until I turn off the truck. Typically, however, there is no indication at all.

I have very limited experience with 4x4 vehicles, and haven't yet had this truck long enough to honestly say I can notice a difference when I am in 2wd vs 4wd. Though it does seem 4wd is engaged and will not disengage. So then my issue is, obviously, how to get it to disengage. I'd greatly appreciated any help on this. And if I am mistaken about it being stuck in 4wd, please enlighten me.

 

I don't notice any difficulty in steering. That's part of why I initially thought it was stuck in 2wd. Though, as I said, I am not yet "used" to this (or any) truck, so I can't say with certainty.

As for the shaft. I just tested it. With the truck supposedly in 2wd or 4wd (button in or out), I can turn the shaft by hand and thus get the truck to move a little.

And for the sake of potential relevance, my truck is a 5 speed manual.

 

I could be getting you wrong, but in 2wd, the front shaft would spin by hand and have no affect on the truck, right? In my case, when I spin the front or rear shaft, the truck moves.

 

In 2WD the front shaft will spin free, front tires won't turn. Sounds like you are indeed stuck in 4WD.

 

Okay, so at least I've got that verified. It's not a good thing, but at least the 4x4 system seems to still be working.

Now I'm assuming one of the actuators is at fault here. I can logically make a case for the ADD actuator or the transfer case one. Where would I start, to figure this out? A guy I know said he should be able to get the wiring diagram for the 4x4 system from work. Should I wait on that and then test for continuity down the line from start to finish? Or is there a simpler, more direct way of figuring it out?

 

So I decided to pull some plugs and do some testing.

First, I pull the power plug from the t-case actuator and tested. Right away, I see that the 4x4 indicator is now lit up and blinking. Makes sense, since the system has no power now. 4lo is still usable but the locker will not engage.

So then I plug it back it and pull the plug on the ADD actuator. 4x4 indicator once again gone. Now 4lo does not work (and thus, the locker will not engage), telling me I should now be in 2wd. What's interesting here, though, is that I can now hear the t-case actuator function when I press the 4wd button on the stick.

From what I can tell, the ADD gets stuck when it has power but does not function when the power is removed. And for some reason, when the ADD has power, the t-case actuator does not function as should and will not engage/disengage the 4x4; I appear to be stuck in 4wd.

Does this tell me that the ADD actuator is not broken (non-functional) but needs servicing to get it to function as should? Or would I need to replace the actuator? I'm guessing the former.

 

I was going to do that, but it seemed to be, more or less, the same as turning the shaft with the wheels on the ground. The truck moves, indicating the front wheels being engaged, yes? Even still, I may as well do it to add further proof for the situation.

Also, I guess I was mistaken with my previous testing? Apparently even with the ADD actuator unplugged, I can still use 4lo. Perhaps it really is just stuck indefinitely and regardless of power feed.

 

best would be to pull the ADD actuator off the front diff and see if it moves when you switch between 4wd and 2wd. If it doesn't move, that's the issue. Some of the older tacomas use a vacuum based ADD actuator along with a solenoids to port air to it. So the actuator may be fine but the lines or solenoids that go to the actuator could be bad.

 

I'll see about doing that tomorrow. I figured I'd pull it off next, but hadn't thought that it might be other parts. I'll have to do some research on what parts work with the ADD actuator and start looking for issues.

 

I'm trying to rule out simpler things before I go pulling PITA things off. So I figured I'd start with electrical. If what I've read is correct, to test the ADD actuator, I pull the connector and test for resistance between terminals 2 and 6, yes? When doing this, it reads no resistance. I also tested the resistance between each of those terminals and a metal ground. Nothing. I shouldn't need to disconnect the battery to get an accurate resistance reading, do I?

Assuming I've done it correctly, and there is no resistance, what would my next step be?
If I've done it incorrectly, how would I go about doing it correctly?