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iPhone Sync Still Fails to Start in iTunes

iPhone SE running iOS 12.0.1

iMac running Mac OS 10.13.6 and iTunes 12.6.2.20


When I connect the phone by cable, it shows up in iTunes. When I hit "Sync", it tries to start syncing but the sync never starts - I get the message: "The iPhone could not be synced because the session failed to start"


I'm syncing / backing up to the Mac - not to iCloud. Also, I rebooted the Mac and the iPhone - no help. The iPhone won’t sync to the computer in iTunes whether I use the Lightning cable or trying to sync over WiFi.


The iPhone synced fine prior to the iOS 12 update. This is my first attempt at syncing running iOS 12. I have an iPad Air 2 running iOS 12 and it syncs fine on the same Mac / same iTunes.


I fixed this problem by re-starting the iMac in Safe Mode, then re-starting the iMac in normal mode, but a few days later, when I again tried to sync the iPhone, and the sync failed to start again.

iMac, macOS High Sierra (10.13.6), 12 GB RAM mid 2010 21.5”

Posted on Oct 17, 2018 9:09 PM

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Question marked as Top-ranking reply

Posted on Nov 3, 2018 6:55 AM

pgoodwin wrote:


I don’t see this in my library:


Finder (~/Library/Application Support/MobileSync/Backup/)

Not sure why you can't find the BackUp folder, I don't believe you can alter it's location without Terminal hacking, so just make sure you are looking in the correct Library, it's the "User" one (ie. under your name).


A comment you made earlier is interesting, when trying to Update to 12.1 a successful BackUp was made, but you could not then do this again manually. Syncing and BackUp are two different processes, you even have two buttons in iTunes for them, "Sync" is bottom right while "Back Up Now" is towards the middle, when you tried the "manual backup" did you still click the "Sync" button or did you try the "Back Up Now" one. You might find the latter works, and if that's so I would guess the issue is purely on the syncing side of things, may be in the form of a conflict in a setting.


You could try selecting your device (top left) and in the sidebar under "Settings" select each category (Music, Films etc) and untick the "Sync" box top left.

User uploaded fileUser uploaded file

When you have unticked everything from Music to Photos under the Settings sidebar, try the Sync process again.


If you still have the same issue after that, then I don't believe you have much option other than try a Restore as New, in other words wipe your iPhone. If you have iCloud syncing enabled on your Mac (or any other device) then when you log back in on your clean iPhone and enable iCloud syncing your data will come back down from the cloud.

User uploaded file

As you can see this can include Contacts, Calendars etc., so you get a good start in getting the device back to how you had it, although you will need to add back your Mail account and obviously download your Apps again.


Hope some of the above helps.

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iPhone Sync Still Fails to Start in iTunes

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