Shutdown and ASD errors on late 2013 15" Retina Macbook Pro My Late 2013 Retina MBP is shutting down randomly. It gets a blank screen, and the keyboard is lit up for about 10 seconds, and then it powers down. There is no kernel panic, and nothing in the logs shows a shutdown. It reboots fine, and generally works for several hours before booting again. 

When running the AST OS tests, I get the following errors:

[01/16/20 17:24:31] AirPort (test #9) - Wireless Module PCIe Root Port Hardware Register Test
- Verifies PCIe root port error bits for wireless module doesn't register any NAKs
[17:24:32]  ERROR - -12100 [IOConnect error reading from PCI address space] -- TEST FAILED
[01/16/20 17:24:32] SATA - 0: SATA PCI Register Test (test #1) - SATA PCI Register Test
- Checks the SATA link error registers for dropped data packets using direct PCI access.
[17:24:32]  ERROR - -12105 [PCI driver IOService open error] -- TEST FAILED


I tried a number of things, but nothing worked:


applied new thermal paste
re-seated the cable from main board to i/o board
re-seated video
put in another SSD drive known to be working
wiped drive and reinstalled Catalina (didn't restore)
reset SMC and NVRAM


The machine has dual graphics, but disabling discrete graphics doesn't help. 

Any ideas on what I can try next, and what the AST test messages mean?
You have a hardware issue.

There are two errors:


ERROR - -12100 [IOConnect error reading from PCI address space] -- TEST FAILED
ERROR - -12105 [PCI driver IOService open error] -- TEST FAILED


Both have to do with I/O (input/output) operations on the PCI bus.  


The first, related to the AirPort card says that it can't read from the "PCI address space."  The address space is a location in memory that points to a physical piece of hardware.  When attempting to read from it, it errors out.
The second, is another I/O error, this time when attempting to connect directly to the SATA hardware; it received an error when trying to open it for operations.


Given that both of these errors related to entirely different pieces of hardware, but both are related in that it's happening on the PCI bus, you have a hardware issue on the logic board.  

Bottom line:  The logic board needs to be replaced.