The contact owns a 2017 GMC Yukon XL. The contact stated that while reversing, the brake pedal became hard and unresponsive. As a result, the contact crashed into a guardrail. There were no reported injuries. There were no warning lights illuminated. The vehicle was taken to the local dealer where it was diagnosed that the brake assist pump needed to be replaced. The vehicle was not repaired. The manufacturer was notified and a ticket was submitted. The contact stated the failure was related to NHTSA Campaign Number: 19V645000 ( Service Brakes, Hydraulic). The failure mileage was approximately 59,000.