These are software-only errors — your iPhone hardware is fine. The problem is with iTunes, your computer, or the settings on your device.

All of these are fixable without any physical repair.

Error 2 — iTunes installation failed (Windows)

Apple Application Support is missing or corrupted. This only happens on Windows. Fix: Completely uninstall iTunes and all Apple components (Apple Mobile Device Support, Bonjour, etc.) → restart → download and install fresh from apple.com (not the Microsoft Store).

Error 4 — Security software is blocking iTunes

Your antivirus or firewall is preventing iTunes from communicating with your device or Apple's servers. Fix: Temporarily disable your security software → try the restore → re-enable it when done.

Error 6 — Can't enter Recovery Mode

The device couldn't switch into the restore mode iTunes needs. Fix: Try a different USB port → restart computer → enter DFU mode manually instead of relying on iTunes to do it.

Error 1015 — Trying to install unsigned iOS

You're attempting to downgrade to an older iOS version that Apple no longer signs, or the device has jailbreak modifications. Fix: Put the device in Recovery Mode and restore to the latest iOS. You cannot go back to older versions.

Error 1110 — Not enough storage

Your iPhone doesn't have enough free space to install the iOS update. This is common with OTA (over-the-air) updates. Fix: Delete unused apps, photos, and videos to free up space. Or update through a computer — iTunes/Finder needs less free space than OTA.

Error 1671 — iTunes is still downloading

iTunes is downloading the firmware file in the background and isn't ready yet. Fix: Just wait. Let the download finish, then try again.

Error 4037 — Device is locked

Your iPhone's screen is locked. iTunes can't update a locked device. Fix: Unlock your iPhone with your passcode, then try again. If you forgot your passcode, you'll need to use Recovery Mode — which will erase everything on the device.

If you've tried everything above and the error keeps coming back, the problem is most likely physical — something broken inside the device that software can't fix. That's when it needs professional hands-on inspection.