There are dozens of threads on the forum about "acquiring signal" on Sirius. Several suggestions point to checking the antenna connection or replacing the antenna. My 2007 CL550 does not have an external roof-mounted antenna, nor an external trunk lid-mounted antenna. Where is the antenna located on this model?

 

I believe it's in the rear window.

 

Not sure about t he W216 but on the W215 it is located under the trunks lid liner since the trunk lid is plastic it does not interfere with signals.

They mounted it there to be out of sight.

 

To resolve the problem, I identified the SDAR model number and purchased a used one on eBay. Swapping out the SDAR, which is in the trunk behind the drivers side panel, did the trick. The other possibility was the antenna (or at least its connection). The mounting of the antenna to the trunk lid, under the lid liner, was confirmed by a MB tech, but did not have to get accessed for my repair. BTW, the SDAR cost $320 on eBay, whereas new from MB was approx. $1,000. Crazy!!