What cable are you using?
There is some confusion because some cables have a different pinout on the DB9 end (I've ordered a wrong one before).

http://opengarages.org/index.php/MCD_software#USB2CAN

The cable mentioned there works great for me. Here's the DB9 pinout of it:

DB9 (DE-9S)
6 Chassis Ground
3 & 5 Signal Ground
7 CAN BUS High
2 CAN BUS low
9 Power

I'm using the USB2CAN for research as part of my thesis.
If you do a project for uni involving a relatively new car it would be great
if you could get in touch. I'm always interested in the implementations
of ISO standards across newer vehicles. Maybe I can help you with some questions as well!

Greetings,
Johannes