2025 yukon AT4 ultimate trans overheating at idle

[GJAngerer]

Thanks for the input and the comparable information, I really appreciate it.
I contacted the dealer yesterday and the ecu had a U0102 code on it.
"Lost Communication with Transfer Case Control Module"
@genestoy those coolant and oil temps seem like they are on the very high end of normal limits.

 

[genestoy]

@genestoy those coolant and oil temps seem like they are on the very high end of normal limits.

You have to remember our ambient temp was 100 degrees, hot here in Arizona this time of year so most likely going to be at the top of the range.

 

[jfoj]

I would also be concerned about the 13.2 MPG Average Fuel Economy as well!

You have a Diesel and unless this thing was idling in gear for a LONG time and the vehicle has not driven anywhere since the Fuel Economy Average was reset something is off here.

My 6.2l gas Yukon has a Lifetime Average Fuel Economy of I think 17.6 MPG.

Something is clearly wrong and it seems the temperatures may be somewhat in agreement?

The Diesel has an external transmission cooling thermostat. I also recall a GM bulletin about kinked cooling lines in the back of my mind. I will see if I can find out if this is a correct recollection.

 

[GJAngerer]

Yes my wife was sitting idling waiting to pick my son up and then sat in a drive thru for a while. We took a trip out to Palm Springs and got 31mpg.
I understand the temps being high when it's 100 plus out, but the day this happened it was 82°F outside and she was idling.
I'm still waiting to here back from the dealer, but I'll post something when they get back to me.
Thanks everyone!

 

[jfoj]

GJAngerer,

This is the bulletin about the twisted transmission lines. While it cuts off at 2024, it is still worth checking this on your vehicle.

https://static.nhtsa.gov/odi/tsbs/2024/MC-10251353-0001.pdf