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I am trying to upgrade from iOS 13.6.1 to 15.3.1, but getting an Unknown Error (4000). I've tried restarting, cleaning up disk space, but nothing seems to work and there is no info found on the help about this specific error code. Suggestions for next steps?
P.S. Could not find iOS Upgrade as a topic choice.
iPhone 7, iOS 13
Welcome to the Apple Support Communities.
Restart your iPhone - Apple Support, then Update iOS on iPhone - Apple Support.
If the issue persists, see: If your iPhone, iPad, or iPod touch won't update - Apple Support.
Jack
I agree, and I have tried to escalate this through the forum hosts several times. 4000, is a very common error code and should be documented. I have a suggestion: Go to these two knowledge base articles:
iOS update and restore errors - Apple Support
Find an iTunes or Finder error code - Apple Support
At the bottom, click where it asks if it was helpful and say NO, and give as a reason that error code 4000 is missing. I’ll do it also.
Error 4000 is an undocumented error code (at least publicly undocumented). It means that the connection between the phone and iTunes was interrupted in the middle of a sync or update activity. In the past this might have been caused by a flakey USB port, an antivirus or a firewall. However, there is a new cause of this error that is the result of a bug in iTunes for Windows that requires the phone not be locked during the update. I think this has been finally fixed in the latest iTunes update, so try getting that from https://itunes.com/. If not first check your antivirus and firewall (temporarily disable them), but if that doesn’t fix it there are three workarounds for the bug:
Note that this error should only be a problem for updates; if you are restoring iOS rather than updating it should not occur.
If you are updating via your computer temporarily disable any VPN and antivirus/antimalware/antispyware software you are using. If you have previously used a jailbroken phone with this computer you will have to correct a file on your computer.
Thank you all for your suggestions. Two steps were required 1) Disabling the autolock and 2) Removing the passcode from my phone (multiple steps here, including disabling BOTH Touch ID & Passcode).
These steps were described in a tutorial from an upgrade to iOS 14, so this generic, undocumented error code has been lingering for awhile.
Documenting errors and giving specific details rather than mapping to 'Unknown error' or any generic error code is a much preferred best practice that would save many users alot of time.
Yes, I did that the first time I went to the link after getting the unknown error.
Steps for Unknown Error Code (4000)
