Hardware Guides stub

PCI Express Downstream Switch Fix – PCI-e Port Won't Detect

Posted on June 6, 2015

Over the course of our recent GTX 980 Ti review, we encountered a curious issue with our primary PCI Express port. When connecting graphics cards to the first PCI-e slot, the card wouldn't detect and resolution would be stunted to lower values. Using one of the other slots bypassed this issue, but was unacceptable for multi-GPU configurations – something we eventually tested.

The Problem

We encountered a yellow bang in device manager (devmgmt.msc) for “PCI Express Standard Downstream Switch Port,” and the failing device corresponded with our first PCI-e slot. This issue arose after performing a driver cleansing; we used a driver cleaning tool to remove all AMD and nVidia drivers prior to benchmarking and, this time, the blast blew away our PCI-e downstream switch port. It may be the case that this is an issue relegated to boards with PLX multiplexing for PCI-e lanes, as our board does utilize a PEX chip to optimize lane switching.

Attempted Solutions & The Fix

We tried a few things to fix this. The first, obvious step was to reinstall all the core motherboard drivers related to PCI-e and the PCH / chipset. We started by reinstalling the Intel chipset drivers, but didn't experience any luck in recovering PCI-e functionality. Attempts to remove and re-install all video drivers in safe mode were also ineffective at fixing the first PCI-e port, though did allow us to connect the card to other slots.

A bit later, we disabled the PCI-e downstream switch port in devmgmt.msc, restarted, and reinstalled the chipset drivers again. Still no luck.

At this point, options were running out. I decided to uninstall the failed device from device manager (right click – uninstall) and reboot, then reinstall the chipset drivers again. At this time, I also went through the Windows update utility to download missing drivers and Windows updates.


The above steps resolved our missing PCI-e downstream switch port problem and got the slot functioning again. If you're having similar problems, give the above a shot and comment below.

- Steve "Lelldorianx" Burke.