IOS – The iPhone “xyz” could not be updated. An unknown error occurred (4000)

erroriosiphoneitunessoftware-update

Using iTunes to update my iPhone, I got:

Das iPhone "xyz" konnte nicht aktualisiert werden. Ein unbekannter Fehler ist aufgetreten (4000)

English:

The iPhone “xyz” could not be updated. An unknown error occurred (4000).

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I could not solve it with the Apple recommended answer at I got Error 4000 when updating iPhone asking you to:

  • update iTunes
  • update the pc
  • plug in the cable directly (I have not done anything else anyway)
  • Restart both pc and iPhone
  • Switch off antivirus and firewall in all possible options

How to fix this? And if there is no fix, which workaround can help?

Best Answer

This is a bug in iTunes when updating iOS via iTunes over USB, where the update will fail if there is a passcode set on the iPhone, and even if the iPhone is in unlocked state when initiating the update.

It exists in version 12.11.3.17 which I am currently on, and also on some of the previous versions (I have no idea in which version this bug originally appeared). I am on Windows 10, 1909 build 18363.904.

The solution is :

  1. connect via USB
  2. temporarily disable the passcode (see below)
  3. update iOS via iTunes
  4. re-enable the passcode

To temporarily disable the passcode :

go to Settings -> Face ID & Passcode -> Turn Passcode Off

>> Face ID & Passcode

Face ID & Passcode

>> Turn Passcode Off

Turn Passcode Off

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