rear view camera issue diagnosing

[olrun]

Hi there. I recently bought a 2015 Jetta TDI SEL. The rearview camera has never worked / black screen. Here is what I have tried so far:
- checked fuses
- new wires between the head unit (RNS 315) and the camera
- new camera
- error code B110231 Rearview Camera - No signal
- the camera has voltage when I switch to the reverse gear

I am thinking about trying a different used RNS 315 unit. Any other options? Are there any inexpensive, reliable aftermarket head units with a rear-view camera?

 

[olrun]

replaced the unit, programmed it with VCDS to enable the camera and have the same black screen when switching to reverse. Does anyone have the electrical diagram for the camera?

 

[pedroYUL]

RCD330+