PCIe slots not working

Tom Rovak

macrumors newbie
Original poster
Mar 2, 2020
I have a Mac Pro 2012 5,1. When I upgraded to Sierra a couple years ago it seems PCIe slots 3 & 4 stopped working. I later went to High Sierra and still those slots are not working. How can I fix this?


macrumors 68000
Dec 16, 2004
Aussie in Japan
No guarantees but worth trying.

Canned air + a brush like this ; clean the PCi slots..

extra_long_soft bristle.jpg


shut down, remove power cord for a few minutes and then all PCie cards including current GPU . .. then . . install the current GPU in a different pci slot.

Now restart using the "Three Consecutive Happy mac NVRAM reset.

IMPORTANT : It is vital to HOLD DOWN the keys illustrated below until one hears the THIRD CHIME.


Worked for me in re-setting my PCIe slots when my GPU(s) were not displaying the correct Link Speed nor Link Width.
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