That is a great question. Usually you can scan the SRS system with a diagnostic scan tool and pull the airbag control module part number. But, if the module is rusted and has water damage then it is most likely has a bad circuit board and is dead. You can try calling the dealership and giving them your vehicle VIN to see if you can get the part number of the module. However, there system may give you a superseded part number that is different from the original part number and it is hard to find a used replacement part with a superseded part number.