4wd System Operation & Help Thread

He said he has 12v on the White/Black wire when checking at the ADD and Transfer case?
But plugged in and back probed, he gets 0v to TL1 and DL1?

Maybe I'm confused on how he checked TL1 and DL1?

Wouldn't the ground (White/Black) be good if checking at the ADD or Transfer case plug?


@aurom709
how did you check for 12v?

 

Maybe I could have been more clear. While back probing at the ECU, with both connectors plugged in and key on, I tested TL1 to ground (white/black), then DL1 to ground, each giving me 12v to ground. The weather was too crappy to check at the t-case and ADD plugs themselves.

 

Ok. Now I understand.
That is a different ground wire than the actuators use.
They use a different ground. We still need to do the check on the actuator plug(s).
The transfer case is the easiest to get to.

Let us know what you find.

Do the test I posted here:
https://www.tacomaworld.com/threads/4wd-system-operation-help-thread.742420/page-44#post-30209777

 

I have a small lift on my rig so getting to the ADD wasn’t so bad.
Alright, so! Tonight’s test:

turned on key, 4lo blinker
At the t-case
TL1 to ground = 0.5v
At the ADD
DL1 to ground = 0.5v
Left both unplugged
TL1 to ground = 6V
DL1 to ground = 6V
Also checked ground to ground from ADD to t-case and continuity is good.

Wife called out to me so I left them unplugged and turned off the key.

Went out to check it all again, turned on key and checked TL1 to ground and 0v. Not realizing that the ECU might not send out a signal because both t-case and ADD were unplugged. So I turned off the key, plugged them both in again, go to check them both in the same order and bam!! 12v to ground on each one while the other is plugged in. Unplugged both, tested each TL1 and DL1 to ground and got 8v.

plugged both back in, turned key off, turned key on, 4lo gone… it resolved itself again. I need to take it for a run to make it happen again, most likely. Unless having both unplugged, turning key on, then off, then plugging them in again reset something when I turned the key on again??? No clue …

When it happens again, I’m just going to have to chase the ground, testing for continuity between teach grounding point from ADD all the way back and t-case all the way back.

 

Wow, that is interesting.
I still think we are dealing with an intermittent ground issue.
The 4WD ECU will provide 12v with the plugs disconnected.

The 6v and 8v part has me thinking there is a wiring/contact issue.

Let's see what @Dm93 thinks.

This is a good one for sure.
We have to figure this one out.
Because we haven't see a problem quite like this one before.....

 

I changed my last name to Murphy this evening. Of course I would get the weird one lol.

 

So I took the truck out for a ride and in about 10mins the 4lo came back on. Drove around for about another 30mins or so, came home, turned it off, flicked they key back over just to see and sure enough, 4lo was gone again!!

Went for another ride for another 20 mins or so and still didn’t come back on. Turned the key on and off, over and over and it still didn’t come back on. I don’t know what to say… the roads are terrible here so if it were a loose connection it should have been shaken loose again. Plus I took it down a pretty rough dirt road just to make it come back. Will keep you all posted.

 

When you say you checked them to ground and had 6v is that to a known good ground or to the White/Black wire?

 

To the white/black at the plug. I strictly tested the plugs only tonight. My plan was to test the plugs themselves, then TL1 and DL1 to a known good ground but I wasn’t able to do that since it suddenly came back to life.

Looks like I have to wait for 4lo again before I can continue.

 

Yea we need to check voltage between Pin 4 (White/Black) at the actuators and a known good Ground with the key on or better yet test light connected to battery Positive to Pin 4 (White/Black) while measuring voltage. We should see less than 0.5v, ideally less than 0.2v.

I'm with @TnShooter I highly doubt both TL1 and DL1 are broken in the same way at the same exact time, an open corroded ground would be more suspect since it is shared.

 

Exactly. Electrically that’s the only thing that makes sense. I just need it to break again so I can trace it back. Since this issue started off as once here and there and lately much more persistent, a bad ground is the only thing that really makes sense. It’s just a matter of finding it.

I only started getting in to this a few days ago and knew nothing about the system until now, but learned a lot as we are going here. Anyone have a wiring diagram and locations of all the ground points and/or splices in this system? I’m fairly certain I know where they are but just so that I’m sure. I would like to test continuity on each ground from point to point, just to look for possible bad splices in the harness before I even attempt at pulling it apart or run a new ground. This rig is a rescue from a bad owner lol.

Really appreciate the help guys. I will be keeping ye posted.

 

A voltage drop test like I described above may give you an answer even if it's not acting up, we can have a poor ground with elevated voltage on it with no symptoms until it reaches a certain point.
It's sort of like a house with a bad neutral connection, as long as the loads are balanced between the two 120v legs everything is happy but when there's an imbalance things go nuts.

We really need to confirm the ground is bad before attempting to fix/run more grounds, also a continuity check is not a good test for checking circuit integrity on any circuits that carry a load. Voltage drop when the circuit is loaded or loading the circuit with an appropriate size test light are much better tests. A circuit can show voltage or continuity and not be able to carry any current as demonstrated in the video below, he's checking a power circuit but the same principle applies to grounds.

https://youtu.be/xazvmJ8_p5Q

 

Yeah, I will be doing that. I will need to make the test light because for me, it’s a little difficult to simply buy one. I live pretty far out there in the middle of nowhere. I had to grind down a set of old meter leads to make my own back probes. In the event that everything else checks out, we are back to the possible broken ground issue.

As for continuity testing, I know that it’s not good for testing integrity under load, what I am saying is that I would like to test from point to point along the ground, throughout the harness simply to find a break or broken terminal. I’m just not sure if I know where all the factory ground points/lugs/bolts, terminals and/or splices are along this wiring harness. For example, detach ground from cylinder head and plug from ADD, then test continuity from ADD to the unbolted cylinder head ground tree, from cylinder head to ECU and so on. If I lose continuity between 2 points then I know the break must be between those 2 points. That’s normally how electricians find a break in a line somewhere, always test between splices and ground lugs as these are usually the culprit. That’s why I would like to know where all these factory splices and bonding/grounding points along the harness.

 

Ok. The best I can explain it. And the easiest way I know how is:

The 4WD ECU supply 12 to DL1 and TL1.
Now inside the actuator we have some light switches.
On of the switches TL1. When the actuator motor turns, it "turns on the switch" and completes the circuit to Ground.
Along the way to Ground, we have a few "wire nuts". These "wire nuts" are in the orange squares I marked in the diagram below.

For the ADD actuator the wire nuts are:
EC1 - Pin 6 (White/Black wire)
PA - Pin 8 - (White/Black wire)
PA - Pin 18 - (White/Black wire)

For the Transfer Case
PA - Pin 19 - (White/Black wire)
PA - Pin 18 - (White/Black wire)

Notice how that PA "wire nut" seems to be a common between the two



Path to Ground through the actuators.

 

Connector and Junction locations - "Wire Nuts"

 

Still unable to do anymore diagnostics on this. Looks like we scared my truck in to working properly. At least now you guys have given me a few methods to start with for when this happens again.

Last weekend I did have the t-case actuator off and apart so I could get a visual and make sure the switch is in the right position. Everything checks out on the pins and internally. ADD seems fine too and switch in the right position. Did a fluid change while I was at it.

Thanks for the walk through. After the rain passes, hopefully this weekend, I will go back underneath and do a visual check at the connection points and where things branch off. I’ll be back with something, I’m sure.

 

A brave man you are....

I wouldn't crawl back under there to check anything.
As soon as you give it any attention, it will act up.

If my stuff is working. I don't even want to talk about it.
Let alone touch it.

I'm just kidding man. Keep us updated.
We'll figure this out. We're 75% of the way there now.

 

I know right! I won’t be going back down there until it acts up again. My rig isn’t so bad to get underneath. It’s got a total of 3” of lift on the front (including tires) so it’s not in my face as much.

It’s kind of funny though… now I want it to be broken. I don’t want to be in a situation where I need 4wd and suddenly it’s not working lol. That’s my luck. We are about to get a lot of rain so who knows, maybe some splashing will get the 4lo back. I will be checking in regularly about this one.

 

Welcome to my world.
It's never broke, until you need to use it.

 

So 4wd is still holding up. No blinky 4lo yet but I still don’t trust it! Again, thanks guys, ye taught me a thing or 3.