Could you tell me how to access the engineering menu in the command unit of 2009 E350 (US model), please? I tried “hang-up + # + 1” combination. That didn’t work. BTW, is there a specific key position (off, 1, or 2) to do that? I would like to make my command unit capable of playing music via Bluetooth. When I try it, it is connecting, but immediately disconnecting with in a fraction of a second. I read about the engineering menu in another forum. Thanks for your help.