Short discription of Class 2 network
Multiplex Engineering, serial to J1850. ~$85 interface. No software.
Card Labs, some J1850 related specs available here.
Adv. Vehicle Tech. listing of J1850 devices. Chips listed here. Complete products are very expensive $800-1500
ScanTool.net $85 interface
ScanTool.net Free software & source code.
more links to specs and data sheets.
Serious prices, but snoops everything.
Vehicle Spy software. $1995
NeoVI vehicle interface for above. $1995
Freediag on sourceforge.