"4WD Off" Message in 4LO - 2024 Silverado, LT, Z71

[Ac3]

Truck:

2024, Silverado LT, Z71, ~12,000 miles

 

Issue:

No power being sent to the front wheels in 4LO with the message "4WD Off" appearing on the dash after rear wheel spin. 4HI and Auto 4WD work as expected.

 

Background:

On my father's farm there is a ~20% grade, grass covered hill which leads to a great view of his property. In my previous vehicles I shifted into 4LO as the gravel road approached the hill and continued my climb without issue. I did the same in my current Silverado, coasting to ~3mph, moving the column shifter to "N", and selecting the "4LO" button. The truck successfully shifted into 4LO as indicated by the dash, the physical sound/ bump of the 4LO planetary engaging, and the increased RPM's associated with LO range.

 

Note that I had not used 4WD of any kind that day prior to this point.

 

I moved the column shifter to "D" and as I started to apply power to go up the grass covered hill, the rear wheels broke loose and I could hear the G80 locker engaging. I stopped and slowly applied power again with the same result. On the 3rd attempt of slowly applying power, the rear wheels broke loose again and the message "4WD OFF" appeared on the dash with the indication it was now back in 2HI. I moved the column shifter to "N", coasted back to the level gravel road, and then put the column shifter to "D" to drive around and see what was up. It was clear the transfer case was in "4LO" as the RPM's were still higher from yet the dash indicated 2HI.

 

I shifted back into 2HI correctly then into 4HI and attempted the hill climb without issue. I went back down to the gravel road in 4HI and gave it some gas to see if I could break the rear end free. I could not, further confirming I was in 4HI. I then shifted back into 4LO successfully and again on the gravel road gave it some gas to see if I could break the rear end free. This time I could, further indicating that power was not being sent to the front wheels despite being in LO range and 4LO as indicated on the dash.

 

Self Diagnosis:

I suspect there is an issue in my transfer case, specifically with the actuator. Since 4HI works, I know my front disconnect is properly engaging, the front differential can transfer power correctly, and that the clutches in the Transfer Case can engage correctly. Since I can shift into 4LO range, I know the planetary gears are working correctly as confirmed by the increased RPM's. I suspect the actuator is failing to properly engage the clutches while in 4LO. There seems to be limited documentation online over my specific scenario. What I could find relates to trucks where their 4WD drive systems are overheating or improperly serviced. As my truck is very new and I had not used 4WD that day, I am ruling out overheating and lack of owner maintenance issues

 

I have a warranty appointment scheduled with the dealer in two weeks where they will give it a full run down. I will post what their findings are here to hopefully help others in the future but in the mean time, I would enjoy hearing from others who may have experienced this or have their own insight into my suspected Transfer Case/ actuator failure.

 

Kind regards,

Ac3 (Ace)

Edited May 22, 2024 by Ac3
Grammer

[Ac3]

A Follow-Up,

 

After being at the dealer for a week, they were not able to re-produce the issue and they did not see any stored codes. They also mentioned the software was up to date and there was nothing they could do at this point other than to look at it again should the issue reoccur.

 

This weekend I was able to take the truck back to the farm to test it again. Lo and behold - 4LO worked just fine! I'm not sure what to think at this point in terms of root cause. I did pull the battery since I had this issue... Perhaps resetting the computer helped the TCCM relearn the proper transfer case clutch engagement?

 

If any others have this issue, let me know as I'd be curious to hear of your symptoms and resolution if any.

 

Kind Regards,

Ac3 (Ace).