Please help, music to car speakers issue.

I have an issue that is either with my Galaxy S4 or my 2008 Saab 9-3. I read that this app has a strong possibility of fixing it, so i'm hoping someone can direct to to the correct settings? My phone has never been able to play music via a standard aux cord to my car speakers. This is the same aux cord i used with my prior HTC phone and i have even tried others so i know the aux isnt the isssue. I just want to plug in the aux cord and play music. Prior to me installing this app whenever i had the aux cord in and the aux setting selected, my phone would only play the music through my phone speaker like it wasnt even recognizing it was plugged in on the other end. Now since installing the app, i hit play and the music simply will not play at all. I'm assuming this is progress. I have the app on the AUX digital setting for both the media and phone audio. Thanks for any help in advance!

Put the media audio on "Let app decide". Aux Digital is actually for HDMI.

Then put a widget on the home screen called "Head set toggle". See if click the widget to the ON position will allow playing music through the wired 3.5mm cable.

Thanks it works! Whenever i change the song though it goes back off, is there a way to make it stay on?

That is strange. What music player are you using?

Just the standard phone player. I go to music then it comes up to all of the downloads I've made.

The S4 may have it's own standard player. For me, the standard player is Google Play Music.

If this is the player, I noticed that it does its own routing to Bluetooth inside the app.
http://www.samsung.com/us/support/howtoguide/N0000003/11205/130842

A lot of the behaviors in these music apps are not controllable from outside the music app. For instance, when the phone rings, some apps pause and continue after the phone call. Other music apps stop the music but don't resume automatically. I've tried doing this in SoundAbout, but what happens is that the default music app can start playing music after a phone call when it wasn't even playing before the phone call began. This is understandably annoying, so I stopped attempting to control what the default music player behavior was doing.