I have a 2010 FX35, my question is are both side mirrors supposed to tilt down when the car is put in reverse? or just one?

On some autos the switch that moves the mirrors needs to be set in the center section vs right or left. On some if its if its to the drivers side and you have it in reverse the mirrors will tilt down.

Mirror Tilt in Reverse Controls
This feature is capable of tilting the passenger side power mirror when the transmission is placed in reverse to provide enhanced visibility during parking or backing maneuvers. This feature is turned OFF or ON through the DIC. The passenger mirror on domestic vehicles can not be changed from the factory setting, but on export vehicles, the passenger mirror position may by changed using the same procedure as the driver mirror. For further information, refer to Driver Personalization in Personalization.

Tilt Mirror In Reverse
Continue with the following steps in order to personalize the tilt mirror in reverse.
Press the Select button in order to enter the menu. The first choice seen is the current setting.
Press the Select button in order to scroll through the following options:
• CURB VIEW: OFF (Default)
• CURB VIEW: PASSENGER
Press the Personalization button in order to advance to the next option.

this might be what you're experiencing.......
Park Tilt Mirrors
If the vehicle has the memory
package, the outside mirrors
have a park tilt feature. This feature
automatically tilts the outside
mirrors to a preselected position
when the vehicle is in R (Reverse).
This allows the driver to view the
curb for parallel parking.
The passenger and driver mirrors
return to their original position
when the vehicle is shifted out of
R (Reverse), or the ignition is turned
off or to OFF/LOCK.
This feature can be turned on or
off through the Driver Information
Center (DIC)

The audio system controls are used
to access the personalization
menus for customizing vehicle
features. (DIC)
CONFIG (Configuration):
Press
to access the Configuration
Settings Menu.
MENU / SELECT Knob:
Press the
center of this knob to enter the
menus and select menu items.
Turn the knob to scroll through the
menus.
0
BACK:
Press to exit or move
backwards in a menu.

Sure hope this helps!
Best to you.

There is a feature on the topend models called something like "Park Assist". It is suppose to tilt the mirror down when you put the vehicle into reverse so the outside mirror will show the curb. This is suppose to help in parallel parking.

The control for this feature is on the Electronic menu. This menu also has the Auto doorlocks, Alarm Chirp, and a few other gadgets. Since the Mirror control is obviously out of control you may try to turn this feature OFF. The Owners manual should show you how. I know that one of the buttons advances the Menu and another changes the setting.

If the Mirror changes settings with the door slamming, then its a problem with the cable running through the doorjam.

350z's have electronic tilting wing mirrors with an on/off position for reverse gear. Some people don't want the mirrors to be adjustable while backing so Nissan put an optional switch on them for enable/disable while the shifter is in reverse position. That is how the car came from the factory. Not sure where that switch is located.

Shift to reverse, adjust the mirror for normal, and save that to memory for that operator. This is presuming that you have not found a setting to turn off reverse mirror settings.....

it is a switch that is not resetting when you take it out of reverse.

On the drivers sidedoor mirror controls put the morror selector to the middle position.

is you question about the auto mirrors for reverse that tilt down and dont come back.
this has been a big problem with these trucks
best thing you can do is turn off the the reverse option