Music files stored on SD card in phone not showing up when connected by USB

[CactusJeff]

I just got a new 2015 Mazda3 Sport today and have been trying to learn the ins and outs of the infotainment system this afternoon. My phone is a Samsung Galaxy S4 and has all the audio files on a 64gb micro SD card and I'd ideally like to connect it via USB so it will charge and allow me to navigate through the music files and folders using the on board system. However, when I plug the phone it it doesn't recognize anything on the SD card. When I try and navigate through the phone's files it's only showing things on the phone storage itself and everything else is greyed out. Is there a setting I need to change somewhere, or is it only possible to access files from the phone itself?

Sorry if this is a dumb question with an obvious answer. I tried googling to no avail as it was a hard search to word.

 

[ebuzzm1]

use bluetooth


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[ALafya]

I tried it only once with similar results.

In short, Android stopped using USB "Mass Storage Device" spec and switched to "Media Transfer Protocol" for many reasons outlined here.
Now, for a long time other vehicles simply supported only Mass Storage Device spec so they would not work with newer Android versions.
It seems like the Mazda 3 does work with MTP but not well. It is able to browse the file system but gets confused and instead of looking for songs it wastes time looking in the wrong places. I hope Mazda will fix this issue.
I did not try to hard to resolve this issue because: 1. My DD is another car. 2. You can always get a simple USB flash device and put your music there. 3. Use Bluetooth.

There seem to be 3rd party apps which re-enable Mass Storage mode, but they don't work on all phones and some require rooted phone (which you will not have normally).
https://play.google.com/store/search?q=mass storage enabler&c=apps