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Error message when you attach a PCI Express expansion chassis to a Windows-based computer: "Code 12" or "Code 31"

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This article provides workarounds for errors that occur when you attach a PCI Express expansion chassis to a computer.

Applies to:   Windows 10 - all editions, Windows Server 2012 R2
Original KB number:   942959

Important

This article contains information about how to modify the registry. Make sure that you back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base: 322756 How to back up and restore the registry in Windows

Symptoms

Consider the following scenario:

  • A PCI Express expansion chassis is connected to a computer.
  • There are devices connected to the PCI Express expansion chassis.

In this scenario, the devices may not be enumerated correctly, or they may not start correctly. Additionally, you may receive one of the following error messages when you view the device properties in Device Manager:

  • Error 1:

    This device cannot find enough free resources that it can use. (Code 12)

  • Error 2:

    The device is not working properly because Windows cannot load the drivers required for this device. (Code 31)

Cause

Cause of error 1

This issue may occur because of the initial state of the PCI Express bridge device in the expansion chassis. By default, when you start or reset PCI Express bridge devices, the initial values of the limit register for the bridge resource window are less than the initial values of the base register for the bridge resource window. This behavior is interpreted as an indication that the bridge resource window is disabled. Additionally, no bridge resource window requirements for the PCI Express bridge device are generated. Therefore, any PCI Express bridge device that requires resources from the bridge resource window will fail enumeration. In this situation, a Code 12 error is generated.

Cause of error 2

This issue may occur if the operating system runs out of Peripheral Component Interconnect (PCI) bus numbers. Typically, the computer BIOS configures a limited bus-number range for PCI Express bridge devices. When an expansion chassis that contains a PCI Express complex switch together with a deep device hierarchy is added to the computer, the operating system runs out of available bus numbers. Therefore, the system cannot start devices in the expansion chassis.

Workaround

Workaround for error 1

Warning

Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk. To work around this issue, follow these steps:

  1. Click Start, type regedit in the Start Search box, and then click regedit in the Programs list.

    If you are prompted for an administrator password or for confirmation, type the password, or click Continue.

  2. Locate the following registry subkey, and then click it:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\PnP\Pci

  3. If the HackFlags registry entry is not present, follow these steps:

    1. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
    2. Type HackFlags, and then press ENTER.
    3. On the Edit menu, click Modify.
    4. In the Value data box, type 400, click Hexadecimal in the Base area, and then click OK.
    5. Exit Registry Editor.

  4. If the HackFlags registry entry is present, follow these steps:

    1. Right-click HackFlags, and then click Modify.
    2. In the Value data box, type 400, click Hexadecimal in the Base area, and then click OK.
    3. Exit Registry Editor.

Workaround for error 2

Warning

Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk. To work around this issue, follow these steps:

  1. Click Start, type regedit in the Start Search box, and then click regedit in the Programs list.

    If you are prompted for an administrator password or for confirmation, type the password, or click Continue.

  2. Locate the following registry subkey, and then click it:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\PnP\Pci

  3. If the HackFlags registry entry is not present, follow these steps:

    1. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
    2. Type HackFlags, and then press ENTER.
    3. On the Edit menu, click Modify.
    4. In the Value data box, type 200, click Hexadecimal in the Base area, and then click OK.
    5. Exit Registry Editor.

  4. If the HackFlags registry entry is present, follow these steps:

    1. Right-click HackFlags, and then click Modify.
    2. In the Value data box, type 200, click Hexadecimal in the Base area, and then click OK.
    3. Exit Registry Editor.

Enable the workarounds for error 1 and error 2 at the same time

Warning

Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

  1. Click Start, type regedit in the Start Search box, and then click regedit in the Programs list.

    If you are prompted for an administrator password or for confirmation, type the password, or click Continue.

  2. Locate the following registry subkey, and then click it:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\PnP\Pci

  3. If the HackFlags registry entry is not present, follow these steps:

    1. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
    2. Type HackFlags, and then press ENTER.
    3. On the Edit menu, click Modify.
    4. In the Value data box, type 600, click Hexadecimal in the Base area, and then click OK.
    5. Exit Registry Editor.

  4. If the HackFlags registry entry is present, follow these steps:

    1. Right-click HackFlags, and then click Modify.
    2. In the Value data box, type 600, click Hexadecimal in the Base area, and then click OK.
    3. Exit Registry Editor.

Data collection

If you need assistance from Microsoft support, we recommend you collect the information by following the steps mentioned in Gather information by using TSS for deployment-related issues.