I just put my old Kenwood KDC-X679 deck in a friends car and the radio works but the cd player and aux won't play audio

https://www.manualslib.com/manual/1055120/Kenwood-Kdc-X679.html?page=26#manual

put a cd cleaner in your cd player see if that helps.

Try selecting aux with the SRC button.

here is the instruction Manual, no point in me stating what they have :)

http://manual.kenwood.com/files/B64-2764-00.pdf

Jennifer, I have the same issue. the problem is that the 2007+ generations of Kenwood receivers are not compatible with the iPhone. You will need to get a 2009+ series in order to use your iPhone with the head unit. I had the same issue with the Kenwood KDC-MP435U in my mustang. I am going to get a newer head unit that supports the iPhone. You cannot do it with the MP435U.

http://www.kenwoodusa.com/UserFiles/File/Global/Consumer/Manuals/KDC-X679.pdf

If a code is required, it was set by previous owner and is 4 digit according to page 26.
http://www.kenwoodusa.com/UserFiles/File/Global/Consumer/Manuals/KDC-X679.pdf

you have to activ ate the aux port form the menu, on standby hold the menu button and then use the control knob on the right to change the aux to on1

it should be in aux try to press source buton and see if that is an option if not an alternative is to hook it up on the back of the cd player in the audio in or aux or aux 2 using a wire adapter from walmart in the car sterio section

for the "AUX input" source put it in standby mode and hold menu... scroll down to "aux in" and turn it on by pushing right