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Reply To: [Solved] Thunderbolt 4 SSD Speeds Throttled to USB 3.0 on macOS Sequoia 15.1: 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 Sequoia 15.1: Diagnostic steps and permanent fix › Reply To: [Solved] Thunderbolt 4 SSD Speeds Throttled to USB 3.0 on macOS Sequoia 15.1: Diagnostic steps and permanent fix

November 14, 2026 at 5:23 pm #8917
Owen Parker
Apple Master (Lvl 10)
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.

Apple Certified Support Professional (ACSP)
Cupertino, CA | "Precision Apple Diagnostics"