Hello.
I believe that you are referring to the Micro Power Module which is installed in the trunk well on E60 5-Series vehicles. It is the power controller for the entertainment, communication, and navigation systems on that vehicle. The most common symptom is the Display screen and radio are inoperative.
If the MPM gets wet it will need to be replaced and often the connector will need to be repaired. After replacement the vehicle will need to be reprogrammed.
Let me know if you need any more information.
Good luck
Scott
BMW Master Technician
BMW Master Technician (Level 1) w/ 8 years BMW experience and 15 years experience overall