The contact owns a 2017 Ford Explorer. The contact stated while driving at various speeds, the vehicle made an abnormal clunking sound, went into LIMP Mode, and failed to exceed 25 MPH. The check engine warning light was illuminated. The contact shifted to reverse(R), but the vehicle failed to respond. The contact called the independent mechanic whom the vehicle was purchased from, but no assistance was provided. The vehicle was taken to a local dealer, where it was diagnosed with catastrophic transmission damage. The contact was informed that the transmission needed to be replaced. The vehicle was not repaired. There was no warranty coverage on the vehicle for the failure. The manufacturer was contacted and referred the contact to the NHTSA Hotline for assistance. The failure mileage was approximately 145,000.