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

[Brenda Johnson]

Diagnostic Hardware Specs: Mac Studio M1 Ultra | OS Version: macOS Sequoia 15.1 | Archive Source: Apple Support Community #256609101

I am running into a persistent issue on my Mac Studio M1 Ultra running macOS Sequoia 15.1.
Whenever the machine encounters Passive cable PCIe link negotiation falling back to USB 3.2 Gen 2, the following diagnostic log appears in Console:

kernel: [IOThunderboltFamily] Port 1 PCIe tunnel timeout - falling back to xHCI 10Gbps bridge

I verified that hardware connections are intact and tested across different power sources. What is the verified diagnostic procedure to permanently eliminate this symptom?

Mac Pro M2 Ultra | Dual Pro Display XDR | Blackmagic UltraStudio 4K Mini | Gothenburg, SE

Final Cut Pro / DaVinci Colorist & Editor | "Verified Apple Discussions Archive"

[Amy Scott]

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″ M2 (16GB) | Glyph Atom Pro 2TB | iPhone 16 Pro Max | Copenhagen, DK

Apple Certified Support Professional (ACSP) | Commercial Photographer & Digitech

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