I just went out and played with mine again, and it does in fact dim when it goes from day to night in the auto mode. On the display setting screen there are 3 buttons. AUTO, DAY, NIGHT. Select the night setting and use the bars on the side to dim the screen. Then select DAY and adjust it to how you want it in the day time. Then hit auto and it goes to what you set it for day and night. To see it work I was sitting in my dark garage. So it started off in the night settings. I put a flashlight on the dash sensor, it takes 15 seconds or so to change. When it does, the nav screen flipped to white and the intensity went up. The blue audio screen stays the same shade of blue but it gets adjusts to the settings that I had made. Worked perfectly.
I have a 2011 and mine doesn't work like that. I don't have the rear entertainment system so the radio and navigation might be a little different.
On mine the auto setting gives control to the dimmer on the dash. It also changes the background automatically from white to black at night.
When in the settings screen and with auto selected you can adjust the dash dimmer and the bar on the side will move and the brightness will change. With the night setting selected the dash dimmer has no effect and the level of brightness is selected by adjusting the bar up or down. Try this. In the settings screen select night mode and set it to the darkest setting and adjust your dash dimmer to the brightest level and then switch to auto. Mine will immediately brighten and the bar will move to what the dash dimmer is set for.
I do have a question for you. The audio system has an automatic volume control compensation setting that will up the volume as you increase speed.
The manual says it has a low, medium and high settings to allow me to adjust the amount of compensation I want. Mine only has on or off. I find that the on setting adjusts the volume to high so I leave it off. I would like to use this feature if I could adjust the level of compensation. Does yours have a low, medium and high setting?