The contact owns a 2016 Ford F-150. The contact stated while driving 60 MPH, the transmission failed to operate as designed and the vehicle unexpectedly downshifted from fourth gear to first gear. The vehicle jerked and made an abnormal grinding sound. The check engine warning light was illuminated. The vehicle was taken to the dealer, who diagnosed a failure with the transmission. The transmission fluid was changed; however, no repairs were made to the transmission. The contact stated that the dealer turned off the check engine warning light. The manufacturer was made aware of the failure, and the contact was referred to the NHTSA Hotline for assistance. The failure mileage was approximately 155,000.