SOLVED! Problems with 4WD

santon

Original poster
Member
Jun 3, 2020
94
Israel
A friend of mine bought a 2006 TB with a problem in 4WD system. There was a "service 4WD" light on and the error code pointing to the front axle disconnect. We put a new front axle disconnect and the actuator; it cleared an error. However, the front axle is still not completely engaged in the "4Hi" mode. We heard some clicks from the front axle and thought that the problem is in the front differential. We replaced the front differential today, and now it seems that sometimes the axle is locked and sometimes not. The "new" differential is supposedly OK; we also crack opened the old one and did not find anything bad with it. With a "new" differential, after several minutes of "tests" on a slippery ground, the system refuses to enter the 4Hi mode and, again, the "service 4WD light appears". As I said, we already replaced the axle disconnect and the differential. What is left is the transfer case... Is there a possibility that the clutches of the transfer are bad and slipping? And, after several minutes of slipping the transfer overheats and does not allow the "4Hi" mode anymore? The problem seems more mechanical than electrical. Do you guys think the transfer case is bad?
 

santon

Original poster
Member
Jun 3, 2020
94
Israel
If you have the ability to read kive data, tell us the voltage of the encoder return when in 4Hi.
Yes, I can read the encoder voltages with Torque Pro (using the PIDs settings that you kindly provided). We also have GM Tech, it also shows the voltages of the encoder. Will observe the voltages and report them on Thursday.

An important observation: when we finished the differential installation, the truck was on the jack stands. We tried to rotate the front passenger wheel, it was locked. So, we thought the problem was solved. Then, during the tests in the mud, we realized that the front axle is not really engaged. Then, after many times of switching between 2Hi and 4Hi, the front actuator stopped moving and the error C0379 appeared. After clearing the error, it was possible to activate the 4Hi mode again. So, my theory is that the clutches inside the transfer case are slipping. Initially the clutches can lock, but the lock is not complete - it may seem OK when the truck is on the jack stands but the clutches start slipping when driving through the mud. As a result, the clutches overheat, the encoder cannot move correctly and sends the wrong voltage signal, and the DTC C0379 appears.
 

Mooseman

Moderator
Dec 4, 2011
25,335
Ottawa, ON
When you replaced the differential, did you also replace the disconnect itself? It could be broken internally. It's on the right side of the oil pan where the CV axle goes in.

Edit: disregard the above. I saw that you replace the actuator AND disconnect.

Maybe there's a break in the wiring for the actuator. Maybe check continuity to the TCCM.
 

mrrsm

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TJBaker57

Member
Aug 16, 2015
2,900
Colorado
As a result, the clutches overheat, the encoder cannot move correctly and sends the wrong voltage signal, and the DTC C0379 appears.

A C0379 DTC does not involve the encoder motor. A C0379 indicates an issue with the front axle disconnect where the expected switch signal does not match the actual switch signal.

Something is not working correctly with the front axle disconnect and/or its' actuator or the wiring between the actiator and the TCCM.
 
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santon

Original poster
Member
Jun 3, 2020
94
Israel
Here are the encoder voltages:
2WD - 2.25V
4WD Hi - 3.63V
4WD Low - 0.76
There are no DTC now, the system switches to 4WD and back. We still suspect some mechanical problem. Will check the wiring though.
 
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TJBaker57

Member
Aug 16, 2015
2,900
Colorado
Here are the encoder voltages:
2WD - 2.25V
4WD Hi - 3.63V
4WD Low - 0.76
There are no DTC now, the system switches to 4WD and back. We still suspect some mechanical problem. Will check the wiring though.


Were these read with a Tech 2? The readings seem a bit low compared to my own readings and tests of several TCCMs I have. The voltage you list as 4Hi would be seen as A4WD in my tests. Your 2WD would be considered neutral. Only the 4Lo falls in the range I have for 4Lo.
 

santon

Original poster
Member
Jun 3, 2020
94
Israel
Were these read with a Tech 2? The readings seem a bit low compared to my own readings and tests of several TCCMs I have. The voltage you list as 4Hi would be seen as A4WD in my tests. Your 2WD would be considered neutral. Only the 4Lo falls in the range I have for 4Lo.
These were the readings with GM Tech 2.

We are still not sure whether the new disconnect locks the axle, so we will run some tests tomorrow. I prepared an aluminum plate with a screw and aluminum "piston"; we will remove the actuator from the disconnect and temporarily place this plate instead of it. The "piston" will lock the disconnect mechanically. If the front axle still not engaged or partially engaged, then the problem is probably in the transfer case (simply because we suppose the "new" differential is OK and the disconnect is locked).
 

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TJBaker57

Member
Aug 16, 2015
2,900
Colorado
we will remove the actuator from the disconnect and temporarily place this plate instead of it.


You can also try placing the system in 4Hi, then raising ONLY the right front wheel off the ground, then with the actuator removed used a large screwdriver and by hand just push in the hole where the actuator plunger would go to see if the disconnect locks. It may require slightly rotating the right front wheel to help the gears align.
 
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santon

Original poster
Member
Jun 3, 2020
94
Israel
Well, it turned out the disconnect/actuator. It is new but not original (made in China). The electrical actuator was not pressing enough on the fork of the disconnect. Finally, we locked the disconnect with a bolt and a plate. The guy bought this TB especially for playing in the mud and sand, so we left the plate permanently. Better solution would be buying a "permanent" disconnect of TB SS, but for now, the bolt will do the job. To prevent the problems with the electrical actuator, it was also removed and replaced with a small device that I built several years ago - a couple of relays and a timer. The device mimics the operation of the disconnect by sending a high or low signal to the TSSM, depending on the incoming command. So, the problem is solved. It seems that the replacement of the differential was not needed.
 

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