I have been in the automotive field for over 25 years and just so happen to own a 2014 Impala ltz. It's the modules in the sides of rear bumper cover. Your rear tires constantly throw water and dirt into the electrical connectors and short them out. Really a dumb design on GM's part. The modules are on intergalactic back order and no dealer near me has parts. However you need to change the modules and harness connectors if you can find them. Good luck 🤞