Skip to content
MappleCare Community ↗

MappleCare Community

[Solved] Mac mini M4 Pro encountering Thunderbolt 4 SSD Speeds Throttled to USB 3.0 after update (macOS Sequoia 15.1)

Find answers from other Apple users or start a discussion about your device.

All Forum Rooms

Home › Forums › MacBook, iMac & macOS Lab › [Solved] Mac mini M4 Pro encountering Thunderbolt 4 SSD Speeds Throttled to USB 3.0 after update (macOS Sequoia 15.1)

Viewing 2 posts - 1 through 2 (of 2 total)
  • Author
    Posts
  • November 15, 2026 at 5:27 am #20443
    Brandon Wright
    Community Contributor
    Diagnostic Hardware Specs: Mac mini M4 Pro | OS Version: macOS Sequoia 15.1 | Archive Source: Apple Support Community #256659139

    I am running into a persistent issue on my Mac mini M4 Pro 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?

    MacBook Pro 16″ M3 Max (128GB) | iPad Pro 11″ M4 (Apple Pencil Pro) | Belfast, UK
    Computer Science & Machine Learning Student | "Verified Apple Discussions Archive"
    November 15, 2026 at 5:27 am #20444
    Lauren Scott
    Community Contributor
    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 Pro 14″ M4 (32GB) | Studio Display | YubiKey 5C NFC | Paris, FR
    Apple Certified Support Professional (ACSP) | Enterprise Mac Sysadmin & Jamf Pro Architect
  • Author
    Posts
Viewing 2 posts - 1 through 2 (of 2 total)
  • You must be logged in to reply to this topic.