The contact owns a 2024 Lexus ES 300h. The contact stated that while his wife was in reverse (R) and backing up into a parking space at approximately 2 MPH, she crashed into the rear of another vehicle. The contact stated that his wife did not hear the rear collision proximity alarm, and the vehicle did not automatically brake. The contact stated that the other vehicle was not damaged, but the contact's vehicle had damage to the driver's rear bumper and trunk. The contact stated that his wife was able to drive the vehicle away. The contact had taken the vehicle to a local dealer, who was unable to duplicate the failure and advised that all collision avoidance sensors were operating normally. The vehicle was not repaired. The manufacturer was informed of the failure. The failure mileage was approximately 23,000.