We have a 2018 Traverse. The check engine light came on and found out it was the converter and leaky flexpipe. We just passed 80K miles when the light came on and missed the warranty. The flexpipe on one side was about $380, but the other side has the converter attached and the price was $1150. Originally this part was separate from the converter, but when they try to find the part, it gets superseded by a newer redesigned part that combined the pipe and the converter.
We haven't fixed it yet, but if we do, it will be our FOURTH pipe/converter since we bought the SUV. The last pipe/converter was replaced in January 2020 and it had a 2 year warranty, which we also just missed by 2 months. Unbelievable that there isn't some class action suit yet for all the people experiencing this. We are trying to work with GM on this but they are almost impossible to communicate with.
To make matters worse, since this all happened in the last few weeks, we were driving it on Thursday and holes blew out in the pipes just behind the Y. Our 2018 Traverse now sounds like a motorcycle. Two symmetrical holes like the pictures above. We think that bracket wore away the pipes and blew out. We are most likely going to do the "tin can" fix until we figure out what to do with the converter. So ridiculous!