Q: iPhone 6 won't sync - unknown error (-4)

Hi Lowey31,

I understand that you are seeing some issues with your ability to sync your iPhone to your computer. Here is an article for you with some troubleshooting steps to help you resolve this issue:

Resolve iOS update and restore errors in iTunes - Apple Support

https://support.apple.com/en-ap/HT201210

Specifically, you may want to pay attention to the suggestions for your error code from this article, as well:

Get help with iOS update and restore errors - Apple Support

https://support.apple.com/en-us/HT204770

Check your security software

Errors: 2, 4, 6, 9, 1611, 9006.

Sometimes security software can stop your device from communicating with either the Apple update server or with your device.

Check your security software and settings to make sure that they aren't blocking a connection to the Apple servers.

 

If you still see the error message, check for USB connection issues.

Take care, and thanks for visiting the Apple Support Communities.

Cheers,

Braden