iTunes Sync Session Failed to Start: Fixes

If you see “iTunes sync session failed to start� on Windows or macOS, the sync process is being blocked before it can begin—usually by a USB driver, a security app, or a corrupted sync preference file. This guide walks you through the most common fixes, from restarting services to resetting the sync history, so you can get your iPhone or iPad syncing again.

What Causes This Error

The error appears when iTunes (or the Finder on macOS Catalina and later) cannot establish a communication session with your device. Common triggers include:

• Outdated or conflicting USB drivers on Windows
• Third-party security software intercepting the connection
• A corrupted iTunes Library.itl or sync history file
• Stale Apple Mobile Device Service (Windows) or a hung usbd process (macOS)
• An iOS device that is locked or has “Trust This Computer� pending

Understanding which of these applies to you narrows down the fix.

Restart the Core Services

The first thing to try is restarting the services that manage the connection.

1. Windows: Open Services (press Win+R, type services.msc). Find Apple Mobile Device Service. Right-click and select Restart. If it’s not running, set Startup type to Automatic and start it.
2. macOS: Quit iTunes (or Finder if using Catalina+). Then restart your Mac. This clears the usbd process that often hangs.
3. Unplug your device, wait 10 seconds, plug it back in, and try syncing again.

If the service fails to start, you may need to reinstall Apple’s drivers (see next section).

Update or Reinstall USB Drivers (Windows)

Windows relies on the Apple Mobile Device USB Driver to talk to your iPhone or iPad. A corrupt or outdated driver is a leading cause of this error.

1. Open Device Manager (right-click Start → Device Manager).
2. Expand Universal Serial Bus controllers.
3. Look for Apple Mobile Device USB Driver. If you see a yellow exclamation mark, right-click it and select Uninstall device (check “Delete the driver software� if offered).
4. Restart your PC. Windows will reinstall the driver automatically when you reconnect your device.
5. If the driver is not listed, install the latest iTunes from Apple’s website (not the Microsoft Store version, which can have driver issues).

If you have the Microsoft Store version of iTunes, consider switching to the standalone installer from Apple—it includes the full driver set.

Reset the Sync History

Sometimes the sync session fails because the previous sync didn’t finish cleanly, leaving a lock file or corrupt history. Resetting this forces iTunes to start fresh.

1. Close iTunes completely.
2. On Windows, press Win+R and type %APPDATA%\Apple Computer\iTunes. On macOS, go to ~/Music/iTunes.
3. Look for a file named iTunes Library.itl or iTunes Library (broken).itl. Move it to your desktop as a backup (do not delete it yet).
4. Also look for a folder named Previous Sync Histories. Move it to the desktop as well.
5. Restart iTunes and try syncing. If it works, you can delete the moved files later. If not, restore them from the desktop.

Note: This does not erase your media or device content—it only resets the sync log.

Check Security Software and Firewall

Antivirus or firewall software can block the local connection between iTunes and your device. This is especially common with suites that include “USB protection� or “network lockdown� features.

• Temporarily disable your third-party antivirus/firewall and try syncing.
• If it works, add iTunes and the Apple Mobile Device Service to the allowed list in your security software.
• On Windows, also check that Windows Defender Firewall is not blocking iTunes. Go to Allow an app through Windows Defender Firewall and ensure iTunes is checked for both Private and Public networks.

Remember to re-enable your security software after testing.

Unlock the Device and Trust the Computer

Your iPhone or iPad must be unlocked when you connect it. If the screen is locked, the sync session cannot start because the device won’t respond to the handshake.

1. Unlock your device and connect it with a cable that supports data (some cables are charge-only).
2. If prompted, tap Trust This Computer on the device.
3. If you don’t see the prompt, go to Settings → General → Reset → Reset Location & Privacy on the device, then reconnect. This clears the trust settings and forces the prompt to appear again.

Also try a different USB port (preferably a rear port on a desktop) and a different cable if possible.

Reinstall iTunes or Update macOS

If none of the above works, the iTunes installation itself may be corrupted. On Windows, uninstall iTunes, then download the latest version from Apple’s website and install it. On macOS, ensure you have the latest macOS update, since iTunes is built into the system (or use Finder for syncing).

Before reinstalling, back up your iTunes library folder to avoid losing playlists or downloads.

Frequently Asked Questions

Why does this happen only with my iPhone and not my Android?

Android uses a different USB protocol (MTP) that doesn’t rely on Apple’s Mobile Device Service. iTunes’ sync is a proprietary protocol, so it’s more sensitive to driver and service issues.

Will I lose my data if I reset the sync history?

No. The sync history is just a log of what was last synced. Resetting it only makes iTunes think it’s a fresh sync, so it may re-copy all your music or photos, but it won’t delete anything from your device or computer.

Does this error occur on macOS Catalina or later?

Yes, but instead of iTunes, the Finder handles syncing. The same causes apply—USB issues, security software, or a locked device—but the fix for services is different (restart the Mac or reset the USB hub).

Can I fix this by restarting my iPhone?

Sometimes yes. A simple device restart can clear a stuck sync daemon. It’s worth trying before more invasive steps.

Is there a way to sync wirelessly to avoid this error?

Yes, if you’ve previously enabled Wi-Fi syncing in iTunes (or Finder), you can sync over Wi-Fi without a USB cable. However, you must first establish a successful USB sync to enable that option.

What if the error appears with a third-party app like iMazing?

Third-party apps use the same Apple Mobile Device Service. If that service is broken, they’ll fail too. Follow the service restart and driver reinstall steps above.

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