4wd System Operation & Help Thread

@Dm93 will be along shortly.
If your front drive shaft is spinning (transfer case locked in 4H) then you have a bad 4WD position switch OR the ground for the switch is bad.

Did you check the ground wire for the switches on the Transfer case?

 

What was the other event that made you start testing the other electrical things like the 4wd system?

 

I’ll also note, that your TL2 never seems to be pulled to GND.
Are you sure the transfer case in in 4WD?

While parked. Go grab the front driveshaft and turn it.
If it turns, it is NOT locked in 4WD.
If it doesn’t turn, it’s in 4WD and for some reason your 4WD position switch isn’t reporting it. Bad switch or Ground.

 

I had my buddy pull the truck forward and peeped under and the front drive shaft rotated.
Have not crawled under and checked either actuator yet. Figured I’d start at the ECU.

…
Lemme preface by saying I’m kind of retarded.


I may or may not have pulled a silly goose and was in a rush and swapped battery leads when jump starting the truck off my other car. Leads were swapped on my car and placed correctly on the truck. Noticed the issue before actually starting up either car and corrected it.
Had a few gremlins that came from that. Went through both fuse boxes and replaced fuses that blew. 4WD fuse was fine when inspected. Upon first start up after this issue, 4WD light and 4Lo were not flashing. It wasn’t until I flipped the switch and the truck tried to go to 4H that it told me Nope.
Truck runs fine and everything else works as of now besides the obvious 4WD system.

As mentioned above, haven’t tried spinning the driveshaft by hand, but did note that it rotated while driving forward. When the front was jacked up, front wheels spun opposite of each other.

 

So your limit switch voltages are correct when the switch is in 2H but you still have flashing lights or they only flash when you tey to put it in 4wd?

 

I'll have to take a closer look later, I'm not home at the moment to sit down and study.

 

It is flashing lights no matter what I do. It truly is angry with me.

 

We all have done stupid shit before when being in a rush but the 2nd mistake I believe was trying to put in 4wd when in park on and incline. I have never tried putting in 4wd in park so I’m kinda wondering if it forced itself into 4wd and maybe out of sync on your transfer case actuator. I’d check your front drive shaft and see if it is locked in or maybe take a drive down the road at low speed and try switching from 2-4H.

 

This is exactly what I think is up. I think the TC actuator is the issue and I think it’s like in between positions with the limit switches being all fucky. I tried pulling off driveway and did the back and forth for about 10 minutes while going through all the positions on the cab switch and I think since the lights flash continuously, the ECU is in the failsafe mode and not allowing shit to happen.

 

Not sure if I posted this before but here are some "Quick Training Guides" for 4WD operation and diagnosis.

I have one more but it says the file is too large.

 

Happy Saturday! What an amazing mass of knowledge, thanks OP!

I would sincerely appreciate some thoughts/guidance on next steps for troubleshooting. I have a '07 V6 4WD. When I put it into 4WD I am met with both the 4H and 4L lights flashing. I performed the voltage test (thanks again for the knowledge!), with details below. When shifting from 2H to 4H, TL1 does not gain voltage and both DL2 and ADD maintain their voltage. I can also hear the Transfer Case actuator making an actuation noise when shifting from 2H to 4H.

I attached an excel with the specific readings. Really appreciate any insights.

 

TL1 doesn’t actually gain voltage.
TL1 TL2 TL3 are all 12v when NOT grounded.

The system is a pull to ground type.
So, when’s ever TL1, TL2 or TL3 are connected to ground (through the actuator) the voltage is pulled to 0v.

Your TL1 wire is being pulled to ground.
Either by corrosion in the actuator motor, or a short on the TL1 wire.

 

Thanks @TnShooter, so would be next step be to check the continuity of the TL1 wire, and if no short, replace the Transfer Case actuator motor assembly?

I appreciate the guidance.

 

I would unplug the connector and check TL1 wire for 12v. (Key on)
If it has 12v, the problem is in the actuator.
If it has less than 12v (such as 1.1v you posted) than the TL1 wire is shorted.

 

Sorry for the delay, I've been out all day. I see @TnShooter has been helping out

Yea it definitely sounds like you have a broken ground wire between EE and Connector PA Pin 18, still haven't had anyone nail down where it breaks but it seems to be a relatively common problem.

 

That's very interesting, so mechanically the system is in 4H but electrically it appears to be in 2H. I don't see how that could be possible, are you sure you were probing the right terminals?
Shifting the 4wd system while in park shouldn't hurt anything, typically if things aren't lined up it just flashes the 4wd light until it's able to complete the shift.

 

If the key wasn't turned on during the mixup I wouldn't think it would have done anything to the 4wd ECU as that is only powered up with the key on.

Definitely seems like it's fully in 4wd then, I think I'd double check the voltages with the switch in 2wd and see what they are one or more of them have to be out of whack.

 

Yeah I had that printout with which terminal is which as well as which color they were and I was saying them out like a schizo.
The only thing I can think of is the ECU noticed something wrong half way to the 4H position and that’s why the limit switches aren’t reading right in 4H/4Lo in the TC actuator. So mechanically it’s operating like it’s in 4wd, but it’s only half locked in if that makes sense? That’s the only thing I can think of. My next option is either backprobe the position switches at the TC or take apart the TC followed by the front diff actuator until I find the issue.

 

I have those posted in the top post.

 

If the TL1 was probed wrong in 2H and was actually 12v. Would that make more sense as to what’s wrong? Then it’d be showing open at each limit switch in all 3 positions.