Q: iTunes could not backup iPhone because the iPhone disconnected

I had a similar problem with my iPhone 6 (iOS 9.2.1) and iTunes (12.3.2)

I tried deleting the previous back-ups, but the problem kept coming back. It got to a point where i could not even backup even after I had deleted the back-ups via iTunes/Preferences/Devices. I had to go into ~/Library/Application Support/MobileSync/Backup to figure out which was the backup for my iPhone and delete that particular folder. Even then, the problem came back after I had backed up the phone once.

I came across another thread and it got me thinking that it could be a corrupted app that is causing the problem. I went through all the apps on my phone to try to figure out which was the one i had installed recently that may have caused the problem. And then i found it. It was an app that i had installed outside of the AppStore. I figure since Apple curates the apps stringently, it is unlikely (but not impossible) that they would allow one in that might corrupt the ecosystem. So i deleted the offending app, and tried again, and lo and behold, everything worked as it should be!

In iTunes preferences - Devices, I had a backup that showed a padlock icon next to it, this was the last backup I made before I had this problem, so I deleted this one (which was quick) and then manually made another backup (which took a while as it was a full backup and I have a lot of pics & music) but this resolved the issue. Thanks a million !!!

I reset all settings on my iPhone and deleted 2 old backups (not the most recent one) and it worked fine afterward.

While deleting either the current backup or the .plist in /private/var/db/lockdown does indeed fix it, this is only a temporary as the issue will return after a few syncs.

Yes I found this happened to me as well, but it doesn't happen every time. Now if I get the same error I try to sync again and it usually works, if not I restart iTunes and/or the PC and so far this has been working for me.

If anyone finds a permanent fix, please let me know.

connecting to the back of the tower seems to have worked. I noticed whenever the fan on the tower would turn on it would disconnect my phone when using the front port

My Case.. just

1. turn off wifi on the phone.. and

2. do the backup again can solve the problem.

hope it helps ~!

after reading a lot ways to fix this i decided to do the two easiest procedures and those seem to work for me.

1- changed the usb port

2- restarted my phone while it was connected to the laptop.

now i don't know which one did it for me but it certainly worked

I know this is a long time ago but I have just spent two days to get a solution for those who may be interested. I have a 4S and tried to back up.on itunes.

Please refer youtube by this guy https://m.youtube.com/watch?v=VyaMU09nuZQ&autoplay=1 It really makes sense.

Plus also I disconnected all from USBs except my mouse sender and switched to flight mode on the phone. At one time i turned off antivirus, but not sure if it was off when I had success. What was obvious once it was working correctly was the thin blue line at the top was slowly increasing in length and took about 3 minutes to extend fully completing the backup.

Before, it went to full length immediately- this indicates it will never backup which I did not understand at the time. Many thanks to the Youtube guy.bpchin

After disabling anti-virus to no avail, this was the only solution that worked for me.

Hi all,

"Could not backup iPad because iPad disconnected" - absolutely infuriating - I've tried every single suggestion in this thread - deleting previous backups in Mobilesync and Lockdown means it gets further in the backup process (45 mins) then crashes out.  Has anybody really got to the bottom of this problem ? I have no trouble with iPhones on the same iMac ...

Cheers Max

In time, all iOS devices get this error. Some cruft isn't purged correctly, seemingly. And all tips posted are only workarounds; no really fix. I've tried everything, and the error always comes back after a couple of consecutive syncs. The only way to fix it is to clean install OSX. But even that is still a workaround, as the error will at some point simply return.

I think the engineers don't have this problem because they clean install much more frequently than their users(?)

Thanks Phil - I've given up for the time being ...

Agree somewhat. In my case, I am pretty sure it was an app (maybe corrupted) that caused it. I started removing apps and found that after a while the sync started working again. It's amazing this still isn't fixed...

If you haven't already, try putting the iPad into airplane mode, or disabling Backround App Refresh (or both!) next time if it's still giving you grief backing up the iPad.

Since you've reset all of the lockdown folder and deleted the previous backup, a likely culprit is that some files are being modified during the backup, causing it to have to back up those files over again. That shouldn't be a problem, except that the backup process tends to crash if it has to "do-over" some files more than twice. I've seen this a lot.