I removed a 12-volt socket in my car and replaced it with a slick USB/ 3.5mm jack that looks close to factory.  I plugged the iPod cord into the USB jack and completed the install. 

 

When I plug a USB stick into the jack, playback and lookup on the head unit work just fine.  But when I plug in an iphone 4 using a factory 30-pin to USB cord, I can control everything on the phone like normal, but there is no volume.  I tried this with two different iPhone 4 handsets and two different Apple brand cords. Same result. I turned the head unit volume up to 35, I made sure the iPhone volume was around 50%, but got no sound at all. 

 

Any ideas?

I removed a 12-volt socket in my car and replaced it with a slick USB/ 3.5mm jack that looks close to factory.  I plugged the iPod cord into the USB jack and completed the install. 

 

When I plug a USB stick into the jack, playback and lookup on the head unit work just fine.  But when I plug in an iphone 4 using a factory 30-pin to USB cord, I can control everything on the phone like normal, but there is no volume.  I tried this with two different iPhone 4 handsets and two different Apple brand cords. Same result. I turned the head unit volume up to 35, I made sure the iPhone volume was around 50%, but got no sound at all. 

 

Any ideas?

 

This particular module you will require the special CD-IU201N cable, since the USB only charges and interfaces between the unit, the audio and video go thru the special port in which the CD-IU201N uses...