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

[Katherine Hunter]

Diagnostic Hardware Specs: MacBook Pro 16″ M2 Max | OS Version: macOS Sonoma 14.6.1 | Archive Source: Apple Support Community #256530024

I am running into a persistent issue on my MacBook Pro 16″ M2 Max running macOS Sonoma 14.6.1.
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?

MacBook Air 15″ M2 (16GB) | GoPro Hero 12 Black | Apple Watch Ultra 2 | Nashville, TN

Digital Nomad & Travel Filmmaker | "Verified Apple Discussions Archive"

[Margaret Wolf]

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

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