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[Solved] Thunderbolt 4 SSD Speeds Throttled to USB 3.0 on MacBook Pro 16″ M2 Max: How to resolve Passive cable PCIe link negotiation falling back to USB 3.2 Gen 2

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Home › Forums › MacBook, iMac & macOS Lab › [Solved] Thunderbolt 4 SSD Speeds Throttled to USB 3.0 on MacBook Pro 16″ M2 Max: How to resolve Passive cable PCIe link negotiation falling back to USB 3.2 Gen 2

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  • November 15, 2026 at 1:43 am #16810
    Lawrence Simmons
    Senior Specialist (Lvl 8)
    Diagnostic Hardware Specs: MacBook Pro 16″ M2 Max | OS Version: macOS Sonoma 14.6.1 | Archive Source: Apple Support Community #256390323

    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 Pro 16″ M3 Pro (36GB) | Studio Display | Magic Mouse & Trackpad | Salt Lake City, UT
    Product Designer & Design Systems Lead | "Verified Apple Discussions Archive"
    November 15, 2026 at 1:43 am #16811
    Sarah Mitchell
    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.

    iPhone 16 Pro (256GB) | iPad Air M2 | Austin, TX
    Apple Certified Support Professional (ACSP) | iOS Product Manager
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