After you try to update or restore your iOS device in iTunes on your Mac or PC, you might see error 53 in iTunes and "Connect to iTunes" on your device.

Error 53 appears when a device fails a security test. This test was designed to check whether Touch ID works properly before the device leaves the factory, and wasn’t intended to affect customers. Error 53 also happens on devices with damaged Touch ID, cause is most likely water damage. DFU restoring to iOS 9.2.1 (13D20) or later will let the device boot but Touch ID will fail to work. Bring the device to Apple if possible. This tutorial is for anyone who experienced error 53. You can try the methods below to solve this iTunes error.

# 1. Solve iTunes error 53 using 3uTools

Download and install the latest 3uTools on PC. Connect iDevice to PC using the USB cable. Choose the available firmware for your iDevice and start to flash.

You’re suggested to choose the latest public firmware version for iDevice, because some beta firmware versions are unstable and even exist unknown bugs, your iDevice may be damaged.

#2. Clear out the Junk

Cache files tend to build up, every time you download and install programs or visit websites. These should be cleared out on a regular basis to ensure your PC is running at peak performance and there’s nothing to interfere with iTunes. After clearing your cache, restart your PC, connect back up to iTunes and try again. 3uTools can help easily clean iDevice's garbage.

#3. Update Windows

This is perhaps the most logical fix. Whenever Microsoft this there is a problem with Windows, it will issue an update so it is vital that you install all of the essential updates on a regular basis. Download and install any that are waiting and then trying iTunes again, to see if the error has been resolved.

#4. Update your PC Drivers

Out of date or corrupted device drivers may be a cause of the iTunes error 53. Ensure that all of your device drivers are fully up to date before trying to update or restore your iPhone through iTunes again.

You could check here for more error codes roundup in 3uTools/iTunes.