2WD to 4WD FAILURE

I figured as much. I'll keep my eyes peeled and let you know if I find anything more helpful.

 

Thanks. I just think this is a Ridiculous situation that Toyota puts us in. IMHO.

 

So the ADD actuator itself is the same as the 2nd gen. However the ECU logic in the 3rd gen that monitors the actuator is MUCH more extensive. I don't believe the 2nd gen would have ever detected the ground fault that you had, unless it got bad enough to blow a fuse. Spoofing the ECU for that actuator is NOT easy without taking 4wd control away from the ECU and doing it yourself. But it isn't impossible, and that is what we have successfully done to create 2Wheel Low on the 3rd gen. If you want help in that regard let me know. I have some research in that area I can dig up.

As your pic shows, you had a short to ground in the motor wires, it appears that corrosion products shorted to ground sufficiently for the ECU to detect. (and probably not enough for the technician to detect when ohming the circuit).

That corrosion is from water sitting in the actuator. The actuator is also the vent location for the front diff, and water seems to get trapped there for several reasons.

Vent tube comes off the ADD (or breaks) and water directly enters the actuator. (This is pretty common)
Water or water vapor enters the top of the vent tube. (Vent tube exit is located on the upper firewall, and is probably very unlikely to have direct water intrusion while driving, but is possible while hosing. However it is certainly possible that water vapor enters here)
Water or water vapor enter thru the seals on the front diff (to the axles on either side or the transmission). (This is certainly possible, but I don't know how probable.)

I assume a contributing cause includes the actuator remaining relatively cold while the front diff gets hot and drives off water, in use which condenses in the actuator.

Also contributing is the very low temp that the diff runs, even while using it. I know @PB FAB had measured temps in only the 140F while in use.... That isn't really going to do much to get any moisture out of there.

So there isn't any great solutions that I know of. Getting rid of the ADD will be very difficult while keeping the ECU in charge.
Working to prevent the corrosion seems more plausible.
I have THEORIZED that it might be smart to put a desiccant in that vent line. It might make sense to add a drain fitting to the actuator itself as well.
And applying corrosionX or similar material inside the actuator may be a good idea.

For now, really my best recommendation is to:
check that vent line on the actuator before and after you do any significant water events
know where the ADD vent is to avoid directly spraying with water

Anything beyond that is just theory... It might be a worthwhile mod to add a drain or water trap to the system, if you are willing to look into it.

 

Any handy diagram links for the ADD vent location?

 

Thanks you for your reply. I’m concern is if I’m out on a trail and need to cross some water and then I have lost 4WD. It had to have been corroded before I cross the water because the failure was within 10 seconds of crossing the stream. I’ll have to come up with something.

Do you know where under the hood the vent is ?

 

found it...post 17 and there’s a few before that too for the tranny and front differential.

https://www.tacomaworld.com/threads/front-diff-transfer-case-and-auto-transmission-breathers.480713/

 

Well that link is way better than the pics I grabbed...

 

That’s some good info there. Thanks for the link.

 

So there is one option, but I don't know if anybody is interested in it.
I have thought about it quite a bit, but never implemented it.

The plug-and-play 2Wheel Low mod as implemented by @lapoltba (https://www.tacomaworld.com/threads...-2wd-low-range-for-the-3rd-gen-tacoma.614743/) installs a plug and play harness between the 4wd ECU and the two actuators. My plan would basically be a mod (an add on) of that harness

The design would consist of 2 dpdt toggle switches located out of the way (in glove box maybe or something) that manually drive the actuators regardless of the 4wd ECU. After turning on the 2Wheel Low switch to apply power to the override circuit, One toggle switch would select the ADD or the transfer case, the second would move the selected actuator in or out. This would move the actuators if there was some level of electrical connection.

This would allow override of the 4wd ECU if there was bad feedback data from one of the actuators. This would also be partially effective for bad connections within the actuators, depending on how bad the connection is. Depending on how bad the short circuit is from corrosion products, this may or may not help.

Just dont know if anybody would actually bother to implement it.

 

My Land Rover Range Rover Velar, has a wading depth of 24 inches per the manual, I would think my Pro could handle that much as well.

 

I replaced my factory front diff breather and ADD breather with ones from @state48overland. It came with my rear diff breather in a kit. The front diff and ADD breather is in your engine bay right next to your fuse box.

 

Thanks Johnny. This is definitely on my list of things to do. The list keeps getting longer.

 

And I've crossed water many many times in my 3rd gen and knock on wood, haven't had any problems with my 4wd yet!

 

Talk to Erick at State48Overland. Super nice guy to talk to on the phone, great prices and shipped fast!

 

Cool. Thanks. I’ll hit them up this week.

 

It’s probably simple. You didn’t happen to recently do a chrome delete? Anyways, pull that panel off as if you were going to replace the knob and check the cable. Can you move the knob into 4 low at all? If not, I know exactly how to fix it

 

^^^
This