2015 cts4 windshield wipers do not operate any other way than the one-time swipe down.

Hello, none of it "sounds right". You'll have to perform needed testing. All diagnostics related to the wiper systems requires scan tool engagement - so I'd seek guidance from a shop with a compatible body module scan tool. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops