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I am not experiencing any disconnects but after five minutes I get a broken up screen display on my Mercedes GLC. There are lots of people experiencing this problem and the common denominator appears be Mercedes and iPhone 17 Pro max. I got a software update from apple yesterday so am hoping when I test it today they have resolved the issue. I still have my iPhone 15 which works perfectly with the car. If it is not resolved this week I am returning my iPhone 17 pro max. It makes no difference if I connect wirelessly or with a cable.
 
same issue wired - 2021 FORD ranger - 17PM w/beta 26.2.1 (switched to beta to see if it would fix, no dice).

I'm experiencing the same as your original post symptoms. It connects then arbitrarily disconnects. Unplugging and replugging fixes it. Stock head unit, nothing between the 17 Pro Max and USB input - and through iOS 18 - my iPhone 14, 15 and 16's (son and wife's) worked for the last four years + (I'm original owner of the FX4 Ranger).

No issues until iOS 26 (I was using the beta public on my 16PM before upgrading to the 17PM)
 
Tested it again this morning after the update to 26.1 yesterday. Slight improvement in that, unless I have full screen maps not seeing the screen breakup anymore. Using either split screen or Icons only no evidence of screen breakup. If I switch the screen to full screen navigation then the screen is distorted and breaks up after about five minutes. The problem can be cleared by switching the information system on the Mercedes off with the switch on the console. But it will always come back after a few minutes. Example of screen breakup attached its like its melting.
 

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