Press the Blue Onstar button. Ask them to read the fault code to you in English and the code number.
If it is something about 'High Voltage charging system...', forget about it.
If the power grid in your neighborhood has a slight glitch, (lightening last night?) while charging you might get a certain fault code.
It goes away on its on after 2-3 full charge cycles.
To feel better about it, pop the hood and check the coolant levels. Top up the windshield washer!
Used '14 2LT w/ DCFC. +85k miles.
Mostly free charging! Only one LONG visit to the shop....
GM needs Modern Troubleshooting tools for Modern EV's.
3 step Trouble Tree, 1st try car died again, 2nd try / cost $800. 3rd try fixed the problem.