What is CAN and why is it important?
CAN stands for Controller Area Network. CAN is a new means of communicating with the car for diagnostics used by the latest generations of VW, Audi, SEAT, and Skoda vehicles. Unlike the older ISO9141 system, which used a single K-line for diagnostic communications, the new CAN-Bus system uses a twisted pair of wires with differential signaling. CAN is considerably faster than ISO-9141 (500 kpbs vs. 10.4 kbps). Both new hardware and new software are required in order to communicate with cars using CAN for diagnostics.

What Cars Use CAN for Diagnostics?
All Golf-5 platform cars (A5 platform)
2003+ VW Touran (1T chassis)
2004+ VW Golf (1K chassis)
2004+ VW Caddy (2K chassis)
2004+ Audi A3 (8P chassis)
2004+ Seat Altea (5P chassis)
2004+ Skoda Octavia (1Z chassis)
2005+ Seat Toledo (5P chassis)
2005+ Golf Plus (5M chassis)
2005+ Seat Leon (1P chassis)
2005.5+ Jetta (1K chassis)
2003+ Audi A8 and A8L (D3 platform, 4E chassis)
2005+ Audi A6 (C6 platform, 4F chassis)
2005+ Audi A4 ("B7" platform) (some control modules)
2005.5+ VW Passat (B6 Platform, 3C chassis)