820-3302-A iMac Late 2012 Slow/Choppy


I upgraded my clients iMac by placing in a SSD silicon power from Amazon. They took it home, then brought it back because the mnotherboard died. The fan would run by itself all the time, even when shut off, but before I replaced this motherboard, the speed was fine. I have done this hundreds of times before, never had an issue until now. I have read about having an EFI driver issue, when I try to load the diagnostics using D or Alt D on the keyboard, this is when I get the error "Error: 0x8000000000000003, Cannot Load 'EFI/Drivers/TestSupport.efi' Status: 0x00000003".
I have tried rebuilding the Fusion configuration which was no help, I have tried finding EFI drivers, could not find any for this iMac (even though I found https://support.apple.com/kb/dl1618?locale=en_US) which was no help since it said this was not for this iMac. I tried removing the original SSD stick from the back of the computer, wiping out the computer, even using a different smaller SSD, of course the PRAM and SMC resets made no difference. I tired running the "sudo trimforce enable", this command did not work.
The reason why I am thinking its an EFI driver issue is because of the EFI driver error above, but I read on a forum that some Late 2012 iMac's when doing the internet recovery will load up Lion, regardless of doing Shift Option Command R, or Option Command R, Option R, all using disk utility to do the Journaled option, and I have tried APFS. I have tried loading from a USB Catalina, Mojave, and High Sierra. Everything is plugged in, the screen is in place, I have never had this issue before. I have looked for any sensor issues but I do not know of any, or what exactly to look for. I tested the SSD's I used and all are 100% healthy (as they should be since each one I have tried is new). Lion if I leave that on there, it seemed to run fine with this. I tried running Hirens boot disk via USB, and Hirens runs super fast with no choppy speed issues. I don't know what else to look for or do. Please help! Thank you.


Staff member
"The fan would run by itself all the time, even when shut off"
The fan requires S0 voltages, can't run in off mode.
Seems that your machine doesn't really go to S5 (off) state; try pressing power button 5s.

Fan still runs high with Lion, or Hirens?

Test flashing known good BIOS, clean ME.
Or try first cleaning actual ME region.