A.D.D. help needed

Hi, I'm new here, been browsing and searching for info lately on new to me, 2000 Tacoma Limited, 3.4, 4wd. 180,000 mi, apparently basic maintenance by previous owner. I've updated all fluids, changed timing belt, belts, hoses, tires, shocks, etc.
Last week I had used the push button 4wd/hi to pull off a logging road to let a log truck pass. Wet grassy road side, on an oil pipeline ROW, I usually engage the 4wd to minimize spinning. No problem, engaged, disengaged when I returned to gravel. A few minutes later I tried to engage it again to park on the side of a road, another routine practice. No luck- no light at all on the dash, no 4wd. I've have used the button a few dozen times prior, always engages within a few seconds.
Troubleshooting to date- mind you, the Haynes manual has been my only shop resource, on line at other times.
Fuse at panel near clutch pedal appears good- swapped with another, checked for power at fuse terminals, good.
Switch on 4 hi/lo lever checked a few times. Today I suspected the wires may have been pinched between the shift lever and the knob, I removed the cable loose jacket, wrapped each wire with electric tape, wrapped all with more tape. I had also bypassed the switch with a jumper wire at the connection closest to the switch, no change.
Front axle actuator removed, appeared generally clean and working, able to move fork with brake bleeder vacuum pump. Oil drained and replaced again, to get dry contact when replacing actuator with gasket material.
ADD solenoids checked, ports appear to open and close when powered, contact cleaner sprayed on connections. (No power found at connections when switch engaged, engine running). Vacuum present in line from intake manifold to solenoid.
Switch at front actuator appears good, continuity when depressed, same with switch at transaxle.
I attempted to remove transaxle actuator, unable to extract it- contacts cleaned there, all appeared intact and generally clean.
It seems to be a lack of power issue, no flashing 4wd light (I checked the bulb and swapped it also) as if trying to engage, just a sudden lack of connection somewhere.
Any ideas at this point? 4wd ECU? it appears this is an unusual fail item, but who knows. Does the vehicle speed sensor weigh in on the 4wd process?
I replaced what i thought was a add relay, passenger side, behind air bag- seems its the power antenna relay- that was working fine, but I guess that will be good to go for awhile....
Any thoughts are welcome.

 

Wow, helluva 1st post. Welcome to TW.

Sounds like you've been quite thorough. Nothing really to offer other than a bump back up to the top.

 

Yep, good job so far.
From your post you have the push button electric actuated transfer and the vacuum ADD. With that combination the 2 most common failures are the 4wd actuator and the 4wd (condition) switch on the transfer.
At this point the following is all I can add, no pun.

Here is the sequence of events that must occur in order to finally get into 4wd.
push 4wd switch on shifter to initiate the transfer actuator, the 4wd (condition) switch determines that the case has physically shifted into 4wd and tells the ECU, the ECU then initiates the ADD thru the VSVs, finally the switch on the diff actuator sees the diff engaged and lights the 4wd dash light

If the actuator works then the front drive shaft should not be free spinning. This is assuming the ADD is not engaged and/or one front wheel is off the ground.
If the actuator is working the 4wd (condition) switch may not be sensing it and the process will stop. Many times this switch will ohm out when manually depressed on the bench but not when on the case due to wear of the plunger and/or the 4wd shifter (in the case). Jump it out and see if the ADD wakes up. If it does try removing the crush washer from the switch and using a dab of sealer instead. This puts the switch just a tad further into the case, effectively giving it a bit more "push". Or just buy a new switch. I have used this technique on the back up light, rear diff lock and the front diff ADD switch, they are all very similar if not the same.

There are write ups on going thru the actuator on this and other forums. They, along with the the electric version of the ADD actuator and the TRD locking rear diff actuator are poorly sealed from the factory and very sensitive to water intrusion.

 

Thanks- If I'm understanding correctly, the switch to change out is the one on the transaxle actuator? And, from your photo, are the two switches shown accessed from the shift lever access cover plate? I'm seeing the DORMAN 600554 in rockauto's catalog, listed as No. 3 Transfer Case Indicator Switch. I'll try that, already have $23 into an antenna relay...

 

My bad. On your model the 4wd position switch is on the actuator itself. You should have a blank plug on the transfer in place of the switch marked "4wd sw" in the picture. Try jumping the switch at the actuator first.
The switch in the pic is accessed from under the truck on the pass side, a real knuckle scraper. Might get it from the top but I never tried.

 

Thanks, I'll try the switch tomorrow am.

 

New switch arrived yesterday, I had time to replace the transfer case switch with the new one, no change. Tomorrow I'm thinking I'll swap the new switch with the front diff.
If no improvement, I'm thinking of removing the transaxle (wow, auto spell certainly changes that word) and get it up on a bench where I can work on it better. I've found a lot on repairing the later model actuators, with the contact solder repair, but I haven't found much on my model. Any tips appreciated.

 

The 4wd actuator can be tested by applying voltage to a couple of pins, at the actuator electrical connector. (I did this on my truck while building it). Unfortunately my brother in law has my FSM. Its easy negative on one pin then 12v to one pin to engage and another to disengage. I'll get my manual and find the pin out for the actuator. Once tested you can rule out the actuator.

 

ok- I saw the diagram in the Haynes for testing it with a heater relay- just haven't gotten together the clips and such to rig it all up- sounds like it's time for that.

 

SUCCESS!!!! After a few weeks of poking around, lots of false starts, hating' the truck, I finally found the cause of the sudden loss of 4wd. I think it was username's post that spells it out- pull the cover off the actuator, clean the yellow cake frosting grease off and clean the contacts, put it back together- 5 minutes, all is well. I did go thru the switches, removed the crush washer, tried that, thanks dirty pool, but it appears to be the three finger contacts on the gear that were the problem- some aluminum corrosion just inside the cover, but no water or other gunk.
I spent awhile with the heater relay test- way too long- I think it is a gullibility test cooked up by a manual writer- at least it nudged me to tearing into the actuator and fixing it.
One new switch in the system now, one power antenna relay updated (!) but back to operational. Also, with all the research, I learned how to engage the rear diff lock, bonus. (truck did't come with a manual, nor maintenance records, which I've since learned, because there was no maintenance). Previous owner stated Toyotas run forever.
I do admit yesterday I spent about as much time on Toyotas site pricing a 2015 rig as I did trying to troubleshoot this one.
Thanks much for the response and the knowledge base on the site.