They make a killing off that though... its a sweet program but the cd they give you is all of like 5MB and the cable is just a chopped usb spliced into a connector to interface with your car, if it wernt for copyright I could reproduce their whole package for like $8

 

What does the chip / board do that's inside the connector then? :-)

 

EDIT: decided to go ahead and explain in some detail...

The device between the usb and the RS232 connectors converts USB to TTL level RS232 signals. All you need to add is a TTL to RS232 converter to provide the +/-12V RS232 logic levels.

its fairly easy to build using fairly common parts...
(e.g. MAX235 Intergrated Circuit, USBMOD1 Hybrid Module)


Now granted its easier to build using more parts (e.g. a case, a board to build it on and such)... but if you solder the wiring directly and wrap it all in heatshrink, or coldshrink it works fine



Or you could just buy a usb/serial adapter for like 14$ then take a serial cable, chop off the other end of it and splice it into the port on your car... making it a serial port, then just plug your serial/usb cable between computer and car, or if u want to go all out install a serial/usb adapter into your car and put a usb port in your dash so you just have to plug your computer into a usb port on the dash

 

Seriously, I didn't know any of that.