How to fix iPhone 6 is not detected or Sync Issues iTunes 12

If your iPhone 6 cannot be detected on iTunes 12 or if you have sync issues, I can assure you that you are not the only one. Many iPhone users experienced the same problem. This issue may show up in both systems, OS X or Windows.

Possible issues:

iPhone 6 cannot be detected by iTunes (OS X / Windows OS)
iPhone can be detected by iTunes, but cannot be detected in Windows Explorer (Windows OS)
iPhone can be detected in iTunes, but cannot syncing (OS X/Windows)
iPhone cannot be detected in iTunes, but can be detected in Windows Explorer (Windows OS)

The Preparation:

Make a backup on your iPhone 6 through iCloud before you do the steps below.

Do also a backup on a Mac/PC just in case the troubleshooting requires you to do something which can disturb the stability of your system.

General Troubleshooting:

Restart the computer
Update the iTunes to the latest version.
Update your operating system to the latest version.
Update iOS on your iPhone 6 to the latest version. See this: How to Update iOS on iPhone, iPad and iPod Touch
iPhone 6 and 6 plus are using lightning cable, try to use the both sides of the lightning cable.
Try to use the other lightning cable, which you know it works well.
Try to use the other USB port

The troubleshooting steps above may solve the issues, but if those solutions didn’t fix the problem try this:

iOS side:

Try to disable restriction if you have activated it.

Go to Settings — General –Restriction — Disable restriction

Windows OS side (Windows 7 or later):

Most of iTunes and iPhone issues occur in Windows OS, try several things below:

Uninstall iTunes and all Apple related software.

Delete the folder C:\Username\UserAppData\Local\Apple and Apple Computer
Install the latest iTunes software, and then restart your computer.