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[Solved] MacBook Pro 16″ M2 Max Thunderbolt 4 SSD Speeds Throttled to USB 3.0 (macOS Sonoma 14.6.1) – Verified Troubleshooting

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Home › Forums › MacBook, iMac & macOS Lab › [Solved] MacBook Pro 16″ M2 Max Thunderbolt 4 SSD Speeds Throttled to USB 3.0 (macOS Sonoma 14.6.1) – Verified Troubleshooting

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  • November 14, 2026 at 10:57 pm #14017
    Leo Koenig
    Community Contributor
    Diagnostic Hardware Specs: MacBook Pro 16″ M2 Max | OS Version: macOS Sonoma 14.6.1 | Archive Source: Apple Support Community #256339132

    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?

    Mac mini M2 (24GB) | Apple Technician Guide Hub | Fluke 87V DMM | Boulder, CO
    Apple Certified Service Technician (ACiT / ACSP) | "Verified Apple Discussions Archive"
    November 14, 2026 at 10:58 pm #14018
    Gabriel Bauer
    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.

    Mac Studio M2 Ultra (192GB) | Universal Audio Apollo x8p | Logic Pro 11 | Munich, DE
    Apple Certified Support Professional (ACSP) | Logic Pro Audio Producer & Mixing Engineer
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