This might be more of an iPhone question than a W212 question, but here goes.

I have an old iPhone 4S that I leave permanently plugged in to the MMI on my 2014 as m,usic storage only. It's been in there a month or two now and other than the file format, which I can't do anything about, it works fine. Always came right up every time I selected "Media Interface".

My car was down for the last two weeks getting the engine rebuilt. Since I got it back, when I try to go to Media Interface, I just get "Device not connected" or whatever the message is. The iPhone ins plugged in, and fully charged, and still continues charging.

I fiddled with it a little bit last night:
- checked connections, they were fine. Plus it's charging so I know the plugs are seated.
- restarted phone, no change
- toggled back and forth between multiple types of media / music, no change.

At one point, in a menu I can't quite recall under Settings, I logged in to something. I think maybe it was "Home Sharing"? It took a good 5 minutes to log in, but then the iPhone worked through the MMI. Great! However, when I turned the car off and back on, it wasn't working again. At this point I had to get home so I stopped playing with it for the night. The phone was charged to 100% the entire time.

I'm not sure what changed here, while the car was in for the engine rebuild. Maybe the phone went dead over the two weeks the battery was removed from the car? But, I guess my question is, do you need to be logged in to something (iTunes, Apple music, or whatever) for it to play over the MMI? When the phone was not connecting, I went in and all my music was where it should be on the phone. When I selected something, it played on the phone, just not through the MMI. I can't see why the car would know if the phone was logged in to something but I'm leaning towards that being the problem.

So my question is what do I need to be logged in to, in order to get the phone to talk to the car? I must have been logged in initially to load the music on the phone, which might be why it worked in the first place. But then, why did that "Home Sharing" login NOT work after I restarted the car? Does that log itself out after a while? Why didn't it do that before?

Thanks for your help. I hope to get some time tonight to play with it a little. I'm sure the problem is related to the phone, not the car or the work that was done on it, but I don't understand what the car needs from the phone in order to get it to play over the MMI.

Thank you!
D