You need a MKIV (DVD-based) nav computer to support the Sirius screen. If you push the MODE button, I believe that it will cycle through to Sirius, but the screen will not display any Sirius info.

Next, you need a BM53 radio manufactured 9/2003 (I think) or newer for Sirius compatibility.

Therefore, these are your actions...

1. Read the part number from your radio. Then check it against the BM53 part numbers in this list to ensure it is one of the radios with Sirius support.
2. Confirm that you have a MKIII nav computer. If you really do have a MKIII, you will need to upgrade to a MKIV.

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SOLD
2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input