Transmission fault light - no actual apparently problem - dealer service diagnosed as "reboot, firmware update" - light goes off - no idea why it was on in the first place
On-star arranged a full main battery swap as my unit was one of several with a known defect (recall)
no other issues beyond those two - but the driver's seat sucks.
Well got back from dealer, said I had 30 codes in multiple modules unknown reason. They stared a case# cleared them all and said if it happens again they will need it for several days. Hopefully they got it on the reset.
Sounds a little like my problems that began with my 12V system. The transmission module was telling the charging system it was in service mode. They updated the software and I think it is fixed. This detailed in another thread tilted 12 V Battery trouble, or something close to that. Bolt 12 volt system troubles