Reports of bricked Wii U consoles have been surfacing more and more over time, with error code : 160-0103. There are various cases of this, both modded and unmodded consoles, as well as partially working consoles but something like Amiibo Settings not working anymore or certain installed game being unplayable to even nothing in system working at all.
The common factor in all these cases seems to be, that the console was turned off for a prolonged period of time. As a preventative measure, the community consensus is to power on the console every now and then, about every month.
Nintendo did not comment on this issue specifically, other than supporting pointing to their FAQ page with this error code. Nintendo also does not service Wii U hardware anymore nor do they supply spare parts.
It is currently not understood what is causing this issue but all signs point to the on-board Samsung KLM8G2FE3B NAND eMMC storage. It seems to suffer from Bit-rot but it is not know whether this is caused by a software issue with the firmware or hardware issue with NAND itself. All firmware versions and hardware revisions seem to be affected by this issue.
There is currently no known fix for this issue. It has been theorized that restore from a good NAND backup could help however, this is not possible by any software method and might never be if the NAND is damaged on the hardware level. Hardware NAND replacement could work but due to the Wii U firmware encryption, there are no known successful attempts. You could try to restore a known good backup and hope the NAND itself is not damaged but this requires additional hardware and microsoldering skills.
If you still have a working Wii U, turn it on every now and then and check if everything still works correctly. If you don’t have a NAND backup currently and don’t mind installing custom firmware, you can follow the guide at https://wiiu.hacks.guide/ to find out how to make a NAND backup. These are always unique, so you can’t use someone elses backup you find on the internet. You need to make your own backup if you ever need to recover it.
If you are experiencing this issue partially, like being unable to use Amiibo Settings or play a certain installed game or anything similar, DO NOT attempt to perform any factory reset. This can be a sign of dying NAND, where factory reset could permanently brick it, so it won’t even boot.
If you are already at the point where your console is bricked, there is nothing you can currently do about it. All may not be lost yet, so don’t throw away your console!