Shortly after taking delivery of this Porsche Approved Certified Pre-Owned vehicle (purchased April 25, 2022, from Porsche Nashua, Nashua, NH), the backup/parking sensors failed to sound. While reversing at home, I waited for the audible warning beep that never came and slowly backed into my own parked 2017 Porsche 911. The Cayenne's door was dented; the 911 was undamaged. A functioning parking sensor system would have warned me and prevented this collision. The vehicle had passed the Porsche Approved CPO multi-point inspection, which is supposed to cover these safety systems. I consider this a safety-related defect in a certified vehicle.