Go get it fixed at the dealer. That was one of my only other gripes with my '17 Sierra when I first bought it (aside from the check engine lights due to faulty nox sensors). After they flashed it the screen no longer brightens after you throw it in reverse with the lights on.I bought a 2017 Silverado and let me tell you its the nicest truck i ever owned, I absolutely love it. However, the navigation/back up screen is terrible at night and can not be dimmed (which is a engineering flaw at its best). Why you can not have this simple option (like completely turning it off, when you do not want it, is beyond me. Tonight prompted me to research after i tried backing up in my normal parking spot, it was raining and If it was not for parking there many times in the past I definitely could not see to park it safely. I noticed there is approximately one inch on both sides of the screen, I am going to put velcro strips there and cut a peice of 1/4 inch plywood that will fit and cover the screen. On the center of the plywood I will attach a handle grip, so you can put it on take it off with ease. Ill store the cover in my center storage area. I hope they correct this error on future trucks. I want to stay with the Silverado and will be looking forward to new one by the year 2020.