SOLVED: 2015 TRD OR Stuck "Halfway" in 4x4 (4LO and 4WD flashing nonstop, NOT the ADD)

Hi All,
2015 TRD OR

I use the 4x4 about once or twice a month so I doubt the issue is for "lack of exercise"

I tried to engage 4lo yesterday (i wasnt paying attention for any indicative noises) and all the sudden the green 4x4 and yellow 4LO lights started flashing nonstop



Since then, it has not stopped flashing no matter the position of the switch. I have done all the "tricks" to get it to engage or disengage, drive straight, neutral with and without brake on, tight turns on soft material, tight turns on hard material, broad sweeping turns, etc, in all positions of the know, with no changes.

The truck is not receiving power at the front wheels. Turns very easy on asphalt.

Also not in "LO gear" as it has no extra torque / low gearing as I am used to

The Front shaft , when sitting in neutral / park / etc , is locked to the rear shaft. I can grab the front shaft and twist back and forth just a TINY BIT and the front and rear shaft rotate in sync.

Therefore leading me to believe the TC is in "4HI"

But no power to the front wheels.

Before I tear into it, any ideas?

I know the common answer is the front diff ADD, but if so, why can't I just get the TC back into 2 HI?

Any thoughts or seen this before?

Last time I used 4wd about 3 weeks ago, no issues, everything worked fine, etc.
Thanks,

 

Sounds like the ADD is disengaged but the transfer case is still in 4H as you suspect.

I'm not familiar with the logic of the 2nd gen flashing indicators but I'd guess either the tcase actuator is stuck or broke or more likely an indicating switch is malfunctioning. It could've done the ADD shift and not gotten confirmation from the switch that it happened so it's holding the current mode.

Check wiring and the switches first, that's easy. I'd go right to the ADD indicator switch. Then dig into the transfer case if that's all good.

 

I've had the 4WD do funky things like this before, but I was always able to fix it by doing the tricks you described (going back to 4HI or 2HI, driving forward a bit, driving back a bit, back to 2HI or 4HI, drive forward a bit, drive back a bit, turn the truck off then on again, turn the steering wheel lock to lock, etc. Not necessarily in the order) Always fixed itself within a minute or two of doing this. Not sure if I was having ADD or TC issues.

 

Thanks man. I think I'll test the two TC "limit switches" because its simple and easy. By ADD Indicator switch, do you mean there is a separate switch I can test that is not part of the overall ADD module?

Yes I tried about all of that, including sitting overnight, but no luck unfortunately. I think it is still trying to complete a shift to 4LO (even though I've moved the dial).

Should probably test the dial switch too, but will check switches on TC first

 

Did you try disconnecting the battery for a few minutes. I know with some electrical glitches that will reset everything. I'm thinking it might need as much as 30 minutes disconnected.

 

Probably should have done that before leaving for work but was trying to get out the door. Driving the unfinished SAS rig in the meantime...

 

No, the switch that communicates the state of the ADD actuator is in the ADD actuation unit.

https://www.tacomaworld.com/threads/how-to-trouble-shoot-4x4-actuator.263525/page-34#post-23596227

 

So it’s a 4x3 right now?

 

If the front wheels don’t turn (get power), but the front drive shaft (while driving) does turn it is the transfer case.
(Or the Front drive shaft does not spin in park)
If you need to get it out of “4WD” you can pull the Transfer case actuator and push the rod all the way IN.

There are 3 positions the rod can be in

All the way out - 4Lo
1 notch in 4High
All the way in 2H.

 

Update and more questions.

Disconnecting the battery didn't do anything. Fuse is good. When fuse is pulled, Christmas tree on the dash.

Checked at the TC first. Found split vent /vacuum (?) Line? Thought it was an easy fix. Cut where it was split and reattached the where it looks like it should go.



No difference I feel like I remember seeing this a few months ago greasing u joints. I dismissed it as an overflow for *something* at the time. Truck has worked in the past in 4x4 with this loose. More on this later

Pulled the limit switches. Both "operate" though I haven't compared to a spec yet. One of them is normally open, when pressed it closes. The other is normal open, but the resistance varies depending how far it is pressed. Thought that was interesting.

Tried to remove TC actuator. Comes out quarter inch and is stuck. Didn't want to beat or pry on it yet. Is this normal, is there a trick to removing? I tried in various orientations.



Anyways, reassembled with switches and bolted actuator. No change.

Off to front end. Broke the plastic right off the actuator trying to remove sizes vacuum fitting. Oops. Guess it'll get a new actuator or a brass barb or something. Heard a "whoosh" of suction when it broke.

Had no trouble getting to the "top left" bolt I see complaints of. For reference, below is the combination of tools I used. 1/4 ratchet to 1/4 to 3/8 adapter to 3/8 drive 12mm socket. Gave me the length i needed without hitting crossmember



Anyways, took actuator apart , nothing out of ordinary looking, no junk inside, terminals look fine, etc. Will solder anyways. All gears and contacts look good though.





I know, I know, I need to go into the formal troubleshooting docs now. But first, my theory. I feel like it has to do with the TC actuator somehow. That vent or vacuum or whatever has been off for a while and operating fine. Is it necessary for normal operation? I feel no.

Anyways, last trip out there was a lot of deep water crossing. Somehow I feel like water got in that fitting and hosed something up.

But I need it to come off first. Any tricks to removing, or is there something more wrong inside the TC if it won't just slide off?

Thanks!

[]

 

Done any driving through water?

 

Yes, partially up the doors for a few hundred feet a month afo

 

You're barking up the wrong tree then. The problem is not the TC it's up front.

Note: I'm basing this entirely on things I've read on this forum. But it seems to happen a lot. The front auto diff disconnect is vulnerable to water, seen it discussed multiple times.

 

The front ADD looks great though. Was sealed up. Looks brand new inside. Plus my symptoms are different than most I've read on here.

Plus the ADD doesn't seem to be the problem, given the fact that the front WHEELS are not engaged, but the transfer case will not come out of 4wd

I stopped at dark tonight but I'm putting my money on the transfer case actuator. Especially if the vent has been disconnected for as long as I believe it has, it's probably full of garbage.

Found on a tundra forum how to get it apart, will tinker some more tomorrow

 

Not necessarily. I'm not 100% sure of the specifics of gen 2 4wd ECU controls but it's likely that if it doesn't sense the front ADD disengaging it won't attempt to shift the transfer case. Basically it goes into a safe mode and stops trying to do things. This doesn't mean the front ADD didn't actually disengage, it just means that the 4wd ECU didn't get the proper signal confirming it disengaged so it doesn't perform the next operation (shifting the tcase back to 2HI). So the problem could be in the ADD system which causes the transfer case to not get a shift attempt.

Now, I'm not saying this is the problem, but it's a likely culprit. The sense mechanism is in the ADD actuator, but the problem could be in the connector or harness. Especially after you got it all wet since this is more exposed than the tcase actuator.

The tcase actuator won't just unbolt and slide out. It's a unit and since the shift rail is pinned to the shift forks it won't come out as a unit without opening up the tcase and removing the shift forks. However, you can open up the tcase actuator housing and carefully disassemble the shift rail from the actuator. There's a pretty good thread here on that I believe.

Get in the tcase actuator and shift the thing by hand, that'll let you know if it's mechanically sound. But what I would do next since it's all apart is find the signal wires from the ADD actuator assembly and confirm what state it's relaying to the 4wd ECU. If it's not signalling that it's disengaged that's the problem. If it's signaling that it is disengaged then I'd dive into the transfer case parts.

 

Thanks, will dig in and follow that path tomorrow and start putting the meter on things. Forgot to put in my post above, I tested the switch in the ADD and it behaved as expected. Need to find a brass barb and seal it up before it goes back into the truck.

 

Good. That only leaves a wiring harness issue for the ADD detection switch. I'd say go on to the tcase actuator and see if it'll manually shift.

 

Look here for manually disassembling and shifting the TC.

https://www.tacomaworld.com/threads/2005-stuck-in-four-low.299498/#post-7599340

 

BTW, if you do this .
Take extreme caution if you follow the part about being in Neutral and rolling the truck.
Don’t run over yourself. I’d use jack stands myself.

 

Thanks much all. Will update everyone after next to keep session and hope this helps someone in the future

Going to try to salvage front actuator plastic with a brass barb, have to see what I can find at home Depot.

Curious what I will find in the rear.