You've connected your iPhone to your computer, put it into Recovery Mode, and initiated a restore. The Apple logo appears on the device with an empty progress bar beneath it. But suddenly, iTunes throws an error window stating: "The iPhone could not be restored. An unknown error occurred (4005)."
Error 4005 is notorious in the iOS repair community. Unlike software signature errors (like 3194) or simple USB glitches (like Error 14), Error 4005 points toward a severe communication breakdown between your computer and the iPhone's core logic board. Specifically, it happens when the device unexpectedly disconnects or reboots in the middle of a critical firmware flash.
What Triggers Error 4005?
To fix Error 4005, you need to understand why the iPhone is dropping the connection. The primary causes include:
- Failing Proximity Sensor / Earpiece Flex: On Face ID iPhones (iPhone X and newer), a damaged or water-damaged earpiece flex cable will cause the device to instantly kernel panic and reboot during the boot process. When it reboots during a restore, iTunes loses the connection and throws Error 4005.
- Failing Battery: If the battery cannot provide a stable voltage during the intense processing of an OS installation, the device will shut down mid-restore.
- NAND / Baseband CPU Failure: If the core storage chip (NAND) or cellular modem (Baseband) fails to initialize, the bootloader will panic and restart the phone.
- USB Controller Issues: Very rarely, a faulty USB controller on your Mac or PC can drop the data packet stream, causing the restore to time out.
Related Guides
If you are troubleshooting Apple firmware issues or managing device updates, explore our other step-by-step guides: