You could always spring $1995 to buy a neoVI. (www.intrepidcs.com). It is bundled with software that will allow you to read raw data from the bus to reverse engineer J1850, CAN, LIN, ISO9141 and others. But this tool is generaly sold to engineers who porgram the ECUs that go into vehicles.
You can also write you own program if you don't like it. You can download it for free at their website, but it won't do you anygood without the hardware.