The contact owns a 2017 Chevrolet Silverado 1500. The contact stated that while driving at an undisclosed speed, the transmission downshifted with several unknown warning lights illuminated. The vehicle was able to be restarted. The vehicle was taken to an independent mechanic but was not diagnosed or repaired. The contact was informed that the vehicle could not be diagnosed due to the check engine warning light not being illuminated. The dealer was contacted. The vehicle was not diagnosed or repaired. The contact was referred to the NHTSA Hotline for further assistance. The manufacturer was not made aware of the failure. The approximate failure mileage was 134,000.