I am far from a transmission expert but I would clear the codes, drive it and see if they come back.

If so the first thing I would do is check all the wiring going to the transmission since its calling a low voltage fault it could either be the sensor itself or a simple wire that's loose or damaged.

These sensors are what tells the ECM to lock or unlock the torque converter as well as shift points. If you're lucky it will be a sensor replacement but it's likely going to need a full rebuild.

Tim

 

I cleared them and will only be able to check them next Saturday.
Meanwhile, today when driving in mode M, I was not able to change gears from the steering... and I was not seeing the engaged gear...
I turned off the engine and it works after...
After couple of kilometers, in drive mode, the 3rd gear was stuck...
I turned off the engine and it works normally after.
I will put it on scanner next Saturday and will keep you posted.

 

This is unfortunately common with the 6L80 transmissions found in the 2008,and 2009 H2's.

Transgo makes a pressure switch repair kit.
The part number is PSR-5. The least expensive place that I have found them is E-Bay oddly enough.

They are somewhat easy to repair, as they are easy accessible by dropping the transmission pan. They are located right on the valve body.

I think the last one I did was less than $15 shipped for the transgo kit.

IF (big if) this doesn't fix the problem you will most likely need a new, used,
or refurbished valve body.
1)make sure you disconnect battery before doing
2)clear codes with key on after reconnecting battery but do not start until after resetting any engine and transmission codes.
If you're using a tech2 it will clear them both at the same time...

 

I see... btw, does this overheat the transmission oil?

 

can you please advise me where i can buy the solenoids?