My 2008 Cadillac CTS transmission will only work in Sport/manual mode?

Hello, I don't think the ice melting has anything to do with your concern. It sounds like either an electronic transmission concern or an internal mechanical transmission concern. Some hands on - diagnostic tool on - testing is required to find out what is happening in each instance. Once operation is checked you'll be able to know a lot more about what's going on inside that transmission. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops