Build:

• i5 6600k

• Team Dark 2x8GB RAM (2133, 2400 OC/XMP)

• Gigabyte GA-Z170X-UD3 (rev 1.0) Motherboard

• BIOS Version for above = F21

• MSI Radeon RX 480 Armor 4GB GPU

• Coolermaster Evo 212 Fan

• EVGA G2 Supernova 750W PSU

• AOC 28" 4K Display

• Windows 10 Home 64 bit

Problem:

I have been having an issue in my new build where, on cold boot or when recovering from hibernation or sleep, my Mobo will report an "IOH Initialization Error" (Error D1 from the manual). I can reproduce the issue with a default bios configuration by doing a hard reset and then quickly (1-2 seconds) starting the machine back up. It will show "D1" reboot a couple times, and goto the BIOS. This only happens on cold boots not on restarts.

When I remove my GPU from the PCI-E slot, I can no longer see the problem.

The interesting thing is, when I get the error and end up in the BIOS, I can reset to any configuration including OC configs, and boot successfully. I believe this is because re-boots from the BIOS are warm reboots and don't require the system to completely shut off and start. Once I'm in I can play games and everything just fine.

I have seen, more than once in this scenario, the BIOS screen flash on for a while, then off, then back on intermittently.

As I understand it, the IOH (PCH) helps provide communication from the PCI-E slot (and other things) to and from the CPU. The symptoms above give me the idea that something is wrong with the stability of the slot or the card, maybe power related.

I've reseated the card once or twice, but I will say that it does have some sag (photos). I was considering getting a brace for it if that was an issue for connectivity.

Has anyone seen an IOH error like this before with a card? Have any suggestions or further tips? I'd hate to pre-maturely RMA my card... Like I said, it appears to work fine after I can get into the system.

EDIT 3/11/2017: For anyone who lands here, the problem was this display port power issue. Basically, my displayport cable I bought off Amazon had a power pin, so it was constantly back-charging from my monitor's power source up through my gfx card, through the PCI-E bus, and into the IOH / PCH areas. This was causing all kinds of problems. I discovered the issue after getting another motherboard with a simple diagnostic LED light instead of a digital code display. I noticed the light was pulsing faintly even when I disconnected ALL power and turned off the PSU switch. Turns out, this was an expensive issue and permanently damaged by Mobo's IOH. I Gigabyte thankfully RMA'd it, and I bought another board. There's a lot of skepticism that this is can cause severe damage or create major disruption, but take it from me, it can.