Error code
iOS 4000
IOS4000
System Error Code· A POSIX/system errno returned when a system call fails.
What it means
Unknown error — iTunes or Finder encountered an unspecified failure during the restore..
How to fix it
- Restart the computer and retry.
- Uninstall and reinstall iTunes on Windows.
- Make sure no other apps are using the device (e.g. iCloud sync).
- Put the device in recovery mode manually and retry.
Not affiliated with iOS. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.
More iOS codes
- 4005Restore failed — a communication error occurred between the device and the host during firmware write.
- 1015Cannot restore to a downgraded firmware version — iTunes detected an attempt to install an older iOS than what Apple currently signs.
- 1110USB configuration or device state error during restore.
- 1394Component or IPSW validation error — iTunes encountered an error validating part of the firmware bundle.
- 14Communication error during restore — the device connection was lost and the IPSW could not be fully written.
- 1600Device not in correct recovery or DFU mode for a custom restore.
- 1601USB driver or host-side communication failure during a recovery-mode restore.
- 1602Connection interrupted at the start of a recovery-mode restore — iTunes could not complete the initial handshake.
- 1604Unknown error during recovery-mode restore — device communication failed partway through.
- 1671Software update is downloading — this code is shown while the device is in the middle of downloading its update.
- 17Device could not be restored to the selected iOS version — the firmware is no longer being signed by Apple.
- 2001USB communication error during restore — the host-side USB chipset returned an unexpected error.