Had to bring my 2017 Volt Premier to the dealer for repair. Check engine light appeared this A.M. after preconditioning while plugged in at a local public charging station. Contacted Onstar twice, once when the check engine light first appeared and again after I drove the Volt home and turned off the car for 15 minutes. When the check engine light reappeared I again contact OnStar. OnStar technical support was unable to receive any remote diagnostics from my Volt. I emptied out inside of the Volt because sometimes these repairs can take days to resolve and I needed my car stuff. My dealer has had the Volt for most of the day, the service adviser called me late this afternoon to let me know that they determined that my Volt has a faulty battery heater core. The part has been ordered, should arrive Monday. I should get my Volt back on Tuesday. I was provided with a 2018? Volt Premier with ACC, Nav as a loaner car. Things could be worse. I will post an update with information on the specific part that was replaced when my Volt has been repaired.