I have the same issue! Did u ever figure out what it was? Here is a little info on mine.
In a nutshell i have a 2010 Chevrolet impala lt flex fuel 3.5l v6, it started just cutting out and when i gave it gas nothing happened, (limp mode). It kept giving me different codes via obd2 scanner. Every few days after I fixed 1 part it would throw another code. After putting a MAP sensor, MAF sensor, Camshaft position sensor, Oil pressure sensor, VVT solenoid, changed oil and filter, it's now giving me a U0100 Loss connection with ecm/pcm "A".
It has always ran and cranked right up until it threw this code about 2 weeks ago. Not it will not crank but has good power. It also will not let me view anything via obd2 now, it only gives me that code. Me not knowing alot about cars, I dont know if my computer is bad or if it's my TCU since they both work hand in hand. I'm so hesitant to put another $1 in this car but it's the only car I have and I have done so much work and put so much money in it already I cant afford not to get it running and start getting back on my feet. From what I have read the "A" has something to do with a short or module not working. I did get a multimeter and done a test best I could on my DLC, here is what I got the first time and the second after I was told my numbers didn't make sense by someone online.
Test #1 in ohms
6&14 was 62.0
4&5 was 1.2
1&16 was 150/160 jumping back and forth
Test #2 in volts
16&1 was 19v
16&4 / 16&5 was 25.1v
16&6 was 21.6
Test #3 Redone Them
6&14 was 62.0 and .03v
16&4 was .33 and 0.02v
6 to ground was 1.00v
14 to ground was 1.00v
6&14 was 88 to 103 jumping and 11.36v
Hopefully u figured out what was wrong with yours and maybe I can check mine for the same issue. Thanks