Uncommanded attempt to shift to 4-LO at highway speed. WTF?

[NWStever]

2022 GMC Sierra 3500 with 6.6L Duramax and 10-speed transmission with 37K miles.   So towing a 5000 lb TT yesterday at 60 mph (after towing without problems for 2 hours) I noticed the dash light drive indicator was flashing 4-Low with a popup warning instructing me to reduce speed to enable shift. I had just used my turn signal to change to right lane when it happened.  No way I brushed the transfer case shift button.  After a few seconds of flashing, the indicator returned to 2WD and the warning disappeared. No repeat for the rest of the tow (approximately 100 miles). I'm a bit un-nerved by this. Has anybody else had this occur.  I'm I getting an early indication of 10-speed transmission or transfer case failure?

[newdude]

1 hour ago, NWStever said:

2022 GMC Sierra 3500 with 6.6L Duramax and 10-speed transmission with 37K miles.   So towing a 5000 lb TT yesterday at 60 mph (after towing without problems for 2 hours) I noticed the dash light drive indicator was flashing 4-Low with a popup warning instructing me to reduce speed to enable shift. I had just used my turn signal to change to right lane when it happened.  No way I brushed the transfer case shift button.  After a few seconds of flashing, the indicator returned to 2WD and the warning disappeared. No repeat for the rest of the tow (approximately 100 miles). I'm a bit un-nerved by this. Has anybody else had this occur.  I'm I getting an early indication of 10-speed transmission or transfer case failure?

 

 

That's a new one.  Its either you brushed the button, which is entirely possible, or you've got a transfer case encoder motor failing.  

 

I'm leaning towards the switch being hit, but I'd scan for codes and see if there is anything that pops up.  

Edited September 3, 2025 by newdude

[Pryme]

The location change of the lighting and transfer case knobs was a poor choice. It would be easier to hit and is harder to see compared to the old location up higher on the corner of the dash. I vastly prefer the location on the 22. Hopefully you just brushed it wothout noticing. 

[PhilB]

I had this exact thing happen to me today.  I saw it and hit the 2Hi button.  I had just been messing with the air vent just before it happened so I knew that I must have hit the button accidentally.  One other time I saw that I was in 4Hi when I had been towing.  Not sure how long it had been in 4Hi, but I figured the switch was hit when I was messing with putting the truck in tow mode.  It is a bad design.

[NWStever]

After some thought and invoking Occam's Razor, I've concluded that I must have brushed the 4WD LO button with my hand after fiddling with the HVAC vent adjacent to the shift cluster.  Thankfully, the truck software prevented the shift.  I'll pay closer attention next time I'm adjusting the vent.