In that case you can press the OnStar button inside the car while running and they can give you the code and tell you within how many days you can put if off before going to the dealership for it.
Before doing anything double check with On Star (via the OS button in the car). Ask them to run a diagnostic check on the car. I got an e-mail from them that they detected an issue with the emission system. There was no check engine light or code on the DIC. OS ran the check with everything coming up OK. Needless to say I was relieved as my car (2017-LT) had less the 1,000 miles on it.