CAN-Bus Shield + UART

Hi guys,

I've been trying to connect my Arduino NANO to a CAN-Bus Shield from SeeedStudio (http://www.seeedstudio.com/wiki/CAN-BUS_Shield)

And i'm failing complety ( the lack of documentation for the shield is a big no).

Just for staters i've been trying to connect to the shield via UART interface (pic):

by connecting directly to a UART/USB converter. But no results, even tweaking the baudrate I can see that the UART/USB device is sending in TX but not receiving even with the Shield connected via DB9 to my car OBD port (and the shield LED for RX from the car is on).

I've no idea what to do next, can anyone help me?