4wd System Operation & Help Thread

But best I can decipher on your chart the voltages are all correct for the system being in 2wd so the ECU should be happy with the switch in 2wd, that's why I'm thinking you missed something.
I'd say put the switch in 2H with the key on, go through the voltages again and post them here. I wanna verify where things are because if those voltages are right there's no way it should be locked in 4wd.

 

According to shift sequence the 4WD detection switch needs to be in the correct position before the A.D.D will be commanded to shift. @Dm93 is a wizard. And might know a better way to check.
But I’d like to know if the transfer case is in 4WD. As your reading say it is not, yet you say the front driveshaft is spinning?

 

Front drive shaft spins as the truck moves forward in gear and the wheels spin opposite when in the air and hand rotated.

I’ll double check the 2wd readings tomorrow to make sure it all checks out. I’ve tried the battery being unplugged for a while and then putting terminals back on with it in 2wd and it still is flashing like the ECU is immediately noticing something is wrong.
ECU must be in the failsafe mode with the constant dash lights flashing cause flipping through the cab switch does nothing to the system.

 

That may explain the flashing light but wouldn't explain it being in 4wd, the mechanical switches (ADD on the diff and 4wd on the transfer case) should both be at 0v if it was mechanically in 4wd unless of course the ground to them was open or the wire between them and the 4wd ECU was open.
I'm wondering if you possibly have an open ground and you just missed the voltage on DL1 because all the other switches are at 12v.
You might want to check the voltage at Connector PA Pins 6, 7, 8, 18, and 19.


Pins should be numbered like this.
22 11
21 10
20 9
19 8
18 7
17 6
16 5
15 4
14 3
13 2
12 1

 

The mechanical switches (ADD, 4wd, & L4) should show where things are mechanically providing their circuits are good.
The limit switches basically tell the ECU where to stop the motors but since the gears are spring loaded they may not necessarily match the actual mechanical position of the Transfer Case and ADD if that makes sense.

 

Yeah, the 4WD switch is physically pushed on by the shift rod.
That’s what has me confused. I don’t see how the 4WD switch can read 11.8v in 4H or 4LO.
Maybe OP is checking the voltages wrong?

 

When I say 4WD switch, I am referring to this one

 

I don’t think I would have probed the same one wrong 3x in a row cause I essentially probed each one in 2H, then went to 4H and worked my way down and then same for 4L. I think I would have gotten something different cause it would have been a different probe each time.

Also where are those harnesses on the truck in that picture. I’d imagine that’s the harness where the wires coming from the ECU are going?

Also explain the PIN numbering like I’m a 4 year old LOL

 

Is there a wrong way to checking them? The diagram I followed has each wire color coded and where they’re at on the harness so I feel pretty good they’re correct. Tomorrow I’m going back to the truck and I can recheck all of em again.

 

Also on a side note, it does make me feel better than I’m not the only one scratching a hole in my head not understanding how this is a thing

 

Or the ground going to it is open, everything else but DL1 is at 12v. If that was a bad reading and it is actually at 12v too then that would indicate to me an open ground circuit.

I'm not saying you did, I'm just trying to think of possible scenarios where the system is mechanically in 4wd but electrically is indicating 2wd and all I can come up with at the moment is an open ground or there was a mistake in testing.

That is at J/B No2 right behind the glovebox.

That should be exactly how they are laid out on the connector as your looking at it so on the left side would be 22 at the top and counting down to 12 at the bottom and on the right 11 at the top counting down to 1 at the bottom. The ones I wanted you the check will all be White/Black wires.

 

I mean if your connecting your meter ground to body ground and the body ground is good (which I would assume it is if everything else works) and your hitting the right pins then the readings should be correct.
I'm really thinking checking those grounds I listed above may be the key to figuring out what's going on.

 

Gotcha now I see where you’re looking I’ll give those a shot when I get back to the truck tomorrow with the fiancé in tow.

So hypothetically speaking, if it was an open ground, wouldn’t this be like a long time issue? Or could it just pop up like this issue did in my case?

Also do you know voltages I should be looking for for each?

Thank you to both of you guys helping me make sense of this. You guys are fuckin rockstars. Hopefully tomorrow I find some answers.

 

0v.

You need to see if they are GROUNDED.
as in continuity to known good body ground.

 

I mean the reverse jump start could have theoretically fried a ground, improper/reverse voltage can do some strange things.

They should be less than 0.1v when checked in reference to a known good ground, anything higher and there is an open or high resistance in the circuit.

 

So if any of those aren’t reading 0v preferably. Is it gonna be a real bitch and a half to find out why it’s not being properly grounded? Or would whichever wire isn’t grounded give an idea location wise where to look for the issue? I don’t have the PA harness in front of me but I’d imagine it’s for sure 4WD switch, L4, and the limit switches that I’ll be checking for?

 

I'm thinking the main ground the feeds the tree (Pin 18) is going to be missing but we shall see.

 

You are checking the ones here.
Follow the wires to see what they go to

 

If you guys manage to Sherlock Holmes this ordeal over this site with my dumb ass feeding you numbers and info, it’ll be like witnessing Jesus break dance on water.


Thank you for your patience and assisting members on here.