The VSP unit is working if the VSP light indicator on the center console-dash is off. (edit: The service manual says that the light comes on and stays on if there's a fault in the system, like for example someone disconnecting the speaker.
Beware, that some cars ship disabled from the factory (probably not yours)... see article below.
It's possible that the previous owner unplugged the VSP unit (Digital Sound Communication Controller Module 285N6-3NF1B) This will turn off the start-up sound as well.
Check to see if it's unplugged. To plug it back in see this video. At the end of the video, simply plug in the white connector. https://www.youtube.com/watch?v=RHWT8VqnRGo
1. VSP speaker part number 28152 3na0a (right below the 12V lead battery) is unplugged and startup sound is disabled thru the instrument gauge menu.
2. VSP unit or speaker pins of the VSP unit is unplugged. Tip: disconnecting the speaker may show some error codes, but not always.
If the speaker unplugs then there's no backup sound. See these pictures for reference http://www.ebay.com/itm/2015-Nissan-Lea ... Sw9GhYbTz9
Beware that there is a DIY in this forum where a relay is tied to the speaker wire and to the backup light, This disables only the backup sound yet nothing else is affected.