The first issue I had was a CEL, our code reader (torquepro on Android) found "3x P26FB: EGR Cooler Bypass Control Stuck Closed Bank 1"
Celeste was running fine at this point, just with a CEL. The dealer techs looked over everything and checked the voltage, cleared the codes and said it might be a fluke.
After a 2nd trip when this happened again, they said the vacuum line was really tight and that they had to bore it out some. We haven't gotten this code since.