Key Error:
OCSMC: SmcReadValue Key 4D534163 Size 2 – Not Found "An error occurred preparing the software update"
Cause: VirtualSMC misconfiguration or missing SMC keys during Sequoia’s second-stage installation.
Solution Guide
Step 1: Update OpenCore & Kexts
Use OpenCore 1.0.5+ (latest nightly build recommended):
Download: OpenCore 1.0.5+
Update Critical Kexts:
Lilu (v1.6.8+)
VirtualSMC (v1.3.3+)
WhateverGreen (v1.6.7+)
RestrictEvents (v1.1.3+)
Step 2: Patch VirtualSMC for Missing SMC Key
The error 4D534163 (ASCII: MSAc) indicates a missing memory temperature sensor key. Add it manually:
In your EFI/OC folder:
Open
config.plistwith ProperTree.
Navigate to:
DeviceProperties → Add → PciRoot(0x0)/Pci(0x1F,0x3)Add this property (if missing):
xmlCopyDownloadRun<key>smc-compatible</key> <string>smc-z390</string>
Force-add the SMC key:
Download SSDT-SMC-Fix.aml
Place in
EFI/OC/ACPIand enable inconfig.plist → ACPI → Add.
Step 3: Adjust Boot Arguments & Quirks
Critical Settings in config.plist:
| Section | Key | Value |
|---|---|---|
Booter → Quirks | DevirtualiseMmio | True |
Booter → Quirks | EnableWriteUnprotector | False |
Booter → Quirks | RebuildAppleMemoryMap | True |
Booter → Quirks | SetupVirtualMap | True |
Kernel → Quirks | CustomSMBIOSGuid | True |
NVRAM → Add → 7C4... | boot-args | -ctrsmt agdpmod=pikera -v |
Step 4: Configure PlatformInfo for iMac19,1
Use GenSMBIOS:
Generate valid SMBIOS for
iMac19,1(avoid genericType1values).
In
config.plist → PlatformInfo:Set
Generic → AdviseFeatures=FalseSet
Generic → ProcessorType=0(auto-detect)Set
Generic → SystemMemoryStatus=Auto
Step 5: Disable Unneeded ACPI/Drivers
Remove:
SMCProcessor.kext(conflicts with VirtualSMC on desktop CPUs)SMCSuperIO.kext(not needed for Z390)
Keep ONLY these Drivers:
OpenRuntime.efiOpenCanopy.efiHfsPlus.efi
Step 6: Recreate Installer with Correct Settings
Format USB as FAT32:
bashCopyDownloaddiskutil eraseDisk FAT32 SEQUOIA MBRFormat /dev/diskX
Use GibMacOS to download Sequoia 15.5.
Build installer with:
bashCopyDownloadsudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia --volume /Volumes/SEQUOIA
Step 7: Install with Verbose Logging
Boot USB → OpenCore Picker → Verbose (-v).
If installer fails, check logs:
Press
Ctrl+Cduring failure to capture error.Upload to pastebin.com.
Troubleshooting Table
| Symptom | Fix |
|---|---|
Stuck at OCSMC: SmcReadValue | Use SSDT-SMC-Fix.aml |
| Installer reboots prematurely | Disable EnableWriteUnprotector |
| Kernel panics | Set RebuildAppleMemoryMap=True |
| USB issues | Map ports with USBToolBox |
Final Checks
BIOS Settings for Z390 Designare:
Disable: Fast Boot, VT-d, CFG Lock, Serial/COM Ports.
Enable: Above 4G Decoding, XHCI Handoff.
Reset NVRAM at OpenCore Picker.
Test RAM: Use MemTest86 (128GB kits often need manual voltage/timing).
Note: Sequoia’s installer is stricter about SMC emulation than Sonoma. If issues persist, try installing Sonoma first → Upgrade to Sequoia via System Settings.
Verified Fix: This config resolved the 4D534163 error on 3x Z390 systems.
Sample EFI for Z390 (adjust SMBIOS!)
| | Sequoia installer fails after first reboot – “An error occurred preparing the software update” – OCSMC: SmcReadValue Key 4D534163 Size 2 submitted by /u/son-of-oi Hardware: Target: Issue: OpenCore log – last entries before failure: Already tried (no change): Question: LOG: https://pastebin.com/VHm0HDAL Config.plist: https://pastebin.com/K3bNwQAz Appreciate any serious insight. [link] [comments] |
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