B codes would be for body codes. As Doc said you will need to know the module to find the code meaning in the Diagnostic Manual. The diagnostic manual is available in print and comes with the WIS. Alldata usually does a pretty good job of copying the MB DM. They probably don't cover all the body modules.
Alldata will do a poorer job on the BMW as there is no print DM for late BMWs; it is part of their DIS or MODIC. BMW does sell some rather inexpensive CDs (from auto technical info standards). They sell a CD called Technical training that covers most BMW systems and codes. Their info can be purchased through their agent: Central Letter Shop in NJ, 1-800-695-0079.
Bosch Master, ASE Master, L1
33 years MB technician