I don't think the BMW CAN bus uses RS485 which could be part of your problem. RS485 is directional so the software will need to take that into account. Almost anything can be made to work but you might be best off to get a specific CAN bus module.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)