I installed this radio in my Chrysler 300c and connected it using a can-bus adapter from Pac-Audio. I also ordered the adapter for the steering wheel remote control from Pac and installed it. Everything works perfectly. According to Pac-Audio you need the C2R-VW2 adapter for a 2003 Passat and the RP4-VW11 for the steering wheel remote control. Apparently the Passat 03 has no output for reverse gear, which means that a reversing camera may not be activated automatically? Info at: https://pac-audio.com
I ordered the adapters in Germany from Maxxcount: https://www.maxxcount.de
Have fun, Peter

Many thanks for the information! It doesn't have a reversing camera. I didn't order a camera either, I just need the adapter where I can control the volume and the channels up and down. Thanks again
LG Simon