i have a 2020 mustang 4 cyl turbo with a shiftable automatic transmission. to give all info the weather was in upper 20's to 30's and we had about 1/2 inch of wet snow. wife got home from work parked the car with parking brake on( driveway is a slight incline no more than 10 degrees), when we woke up next morning the car had moved backwards about 6 feet. i chalked it up to the fact the wet snow froze with heavy winds and maybe the car just slid. we drove the car that afternoon and when we got home i put on parking brake after putting it in park and got out. the wife started getting and and said the cars rolling, i turned around to see it roll about 2 foot. i hadnt even closed the door yet also i noticed that the back tires were moving as if it was left in a high gear of a manual tranny. its the weekend and just looking for ideas before i call the dealership on monday.

 

It's a new car in warranty. Take it to the dealer.

 

yeah dealer. If you put into 'park' and engaged the parking brake, the rear wheels should NOT be rolling. Sounds like both the e-brake is frozen in place (happened on 2005/2006 mustangs) and the Transmission isn't engaging the parking pawl. No idea how accurate that guess is.