iPhone error 4013 is a hardware issue that disrupts the connection between the motherboard and the nand chip, often appearing during updates or restores. To resolve this error, users can update iTunes, check USB connections, disable security software, try a different computer, perform a force restart, update iPhone software, restore in DFU mode, or consider a factory reset. If these steps do not solve the problem, it is advisable to seek assistance from an Apple store or authorized service provider.