Default In car audio via USB only works on AOSP based ROM?

Hello, so I've had my G2 for quite a while now, and ever since I got it I have had Paranoid android on it (got it off a craigslist trade, had CM10 installed when he gave it to me.) I recently started using the Flex based ROMs though. My question is, why is it that when I connected my phone up to my car's usb port while I had PA 4.4 on there, the car would read my SD card and make a list of my songs that I could control via my steering wheel and the radio itself, but when I switch over to a Flex based ROM, it doesn't do this anymore? I have USB debugging on and I mounted MTP. Thanks in advance!


P.s. in case this helps, I have a bottom of the line, completely stock 2013 Chevy Cruze.

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