I push my initial sketches for Arduino on my github page: https://github.com/manu-t/autoradio-interface
UpdateListDisplay.ino is the initial sketch to drive the canbus Renault display. It has a serial interpreter for commands. The displaySong() function gets the song title from the serial stream and displays it (scrolls text if more than 8 characters). I intend to use a bluetooth bee (spp bt module in xbee format) instead of the serial uart USB, but haven't tested it yet.
HID_rn42_dpad.ino takes inputs from the Renault steering wheel remote control, the C&K dpad and send it to the smartphone as key inputs.
I have to tidy up this code to keep the essential part (some stuff has to be removed), but as it is it is functional.