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Reply To: [Solved] Thunderbolt 4 SSD Speeds Throttled to USB 3.0 on macOS Sonoma 14.6.1: Diagnostic steps and permanent fix

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Home › Forums › MacBook, iMac & macOS Lab › [Solved] Thunderbolt 4 SSD Speeds Throttled to USB 3.0 on macOS Sonoma 14.6.1: Diagnostic steps and permanent fix › Reply To: [Solved] Thunderbolt 4 SSD Speeds Throttled to USB 3.0 on macOS Sonoma 14.6.1: Diagnostic steps and permanent fix

November 14, 2026 at 11:10 pm #14248
Margaret Wolf
Senior Specialist (Lvl 8)
Apple Recommended / Verified Community Solution
This canonical solution was verified and marked as solved in the Apple Support Community archive.

Verifying certified 40Gbps active cables, resetting Thunderbolt kernel extensions, and enabling TRIM.

Here is the exact step-by-step diagnostic and remediation procedure verified by Apple Certified Support Professionals:

  1. Verify cable has official Thunderbolt 4 lightning bolt and ‘4’ logo. Charging cables will not negotiate PCIe.
  2. Reset bus enumeration: sudo killall -9 diskarbitrationd.
  3. Enable APFS TRIM support: sudo trimforce enable.

Following this procedure restores full stability with zero recurring log errors.

MacBook Air 15″ M3 (24GB) | CalDigit TS4 Dock | Kensington Orbit | Minneapolis, MN
Apple Certified Support Professional (ACSP) | Enterprise Mac Sysadmin & Jamf Pro Architect