One of the back up sensors is not working. Not sure how to tell if one is bad. Bought a new sensor.. pretty pricey 185.00 need. to know how to get display to stop reading : service park assist?" 2007 Chevy Avalanche

 

Have you checked to see if you still have an existing bumper-to-bumper warranty? The sensors would be covered under that and you should be able to take your truck into the dealership and fixed free of charge.