ODB just reads engine data. It was mandatory for MB to do this on USA cars. On a typical 140 or 220, it cannot read the other 5 CAN busses' on the network. You won't see ARS, SRS etc - that's reserved for the "other" code readers.

I've seen off-brand code readers that claim to read MB CAN bus in the form of a laptop, a Linux kernel, Palm Pilot, even on on your wrist watch. The only one I've seen that invariably shows ALL and correct data is WIS. Subscription is [somebody help me with this] like $12k/yr per unit. A typical shop will have 30-40.

Sometimes you'll see the DVDs for WIS on Ebay or something, like someone from the shop made a copy. But they've got all sorts of tricks for copy protection and user-keys, which change all the time to keep out the riff-raff.

If I absolutely have to have WIS, like a motor change, iginition modules, computer modules, transmission diags etc - I'll just pay my $100 and be done with it. They always gladly print a detailed history, plus reset 0's