Fix PCI Serial Port Driver Issue in Windows

If you see a “PCI Serial Port” device with a yellow exclamation mark in Device Manager, Windows is missing the driver for your motherboard’s serial (COM) port controller. The fix is to identify the exact hardware ID and install the correct driver, usually from the chipset manufacturer (Intel, AMD, or a third-party like ASMedia or Fintek) or your motherboard vendor.

What Causes the PCI Serial Port Error

The “PCI Serial Port” entry appears when Windows cannot find a driver for a serial port controller that is not natively supported. This is common after a fresh Windows installation, a motherboard BIOS update, or when Windows Update fails to deliver the right driver. The controller itself is often part of the chipset (e.g., Intel’s Serial IO or AMD’s SMBus) or a separate PCIe card. The error means the hardware is detected but has no functional driver, so the COM port is unavailable for devices like barcode scanners, GPS receivers, or industrial equipment.

Step 1: Identify the Hardware ID

Before downloading anything, you must know the exact device. Windows shows a generic name, but the hardware ID reveals the vendor and model.

Open Device Manager (right-click Start → Device Manager).
Find “PCI Serial Port” under “Other devices” or “Ports (COM & LPT)”.
Right-click it → Properties → Details tab.
In the “Property” dropdown, select “Hardware Ids”.
You’ll see lines like PCI\VEN_8086&DEV_9D3E&SUBSYS_.... The VEN_ is the vendor, DEV_ is the device number.

Write down both the VEN and DEV values. For example, VEN_8086 is Intel, VEN_1022 is AMD, VEN_1B21 is ASMedia.

Step 2: Find and Install the Correct Driver

Once you have the hardware ID, you have several options. Try them in order:

Windows Update (optional): Right-click the device → “Update driver” → “Search automatically”. This works occasionally but often fails for niche serial controllers.
Motherboard vendor’s website: Go to the support page for your exact motherboard model, download the chipset or serial IO driver, and install it. This is the most reliable source.
Chipset manufacturer: If you know the vendor (Intel, AMD), download the latest chipset driver from their site. Intel’s “Chipset INF Utility” and AMD’s “Chipset Software” often include serial port drivers.
Third-party driver sites: Sites like Station-Drivers or the manufacturer’s own support forum may have specific drivers. Be cautious—only download from reputable sources and scan files.

After installing, restart the PC. The yellow mark should disappear, and the device should appear under “Ports (COM & LPT)” with a COM number.

What to Do If the Driver Won’t Install

Sometimes the driver downloads but fails to install. Common reasons and fixes:

Wrong architecture: Make sure you downloaded the 64-bit (x64) driver if your Windows is 64-bit (most are).
Driver not signed: If you get an “unsigned driver” warning, you may need to disable driver signature enforcement temporarily (Advanced Startup → Troubleshoot → Startup Settings → option 7). This is a temporary fix—re-enable it after.
Manual install: In Device Manager, right-click the device → “Update driver” → “Browse my computer” → “Let me pick from a list” → “Have Disk” → navigate to the extracted driver folder. This forces Windows to use the driver you downloaded.
Remove and rescan: Right-click the device → “Uninstall device” (check “Delete the driver software” if available), then click “Scan for hardware changes”. Sometimes this clears a corrupted driver state.

Common Misconceptions and Pitfalls

Many users assume the “PCI Serial Port” is a legacy COM1 port that Windows should handle automatically. That’s true for the traditional 16550 UART, but modern systems use a different controller (like Intel’s Serial IO or a Super I/O chip) that needs a specific driver. Another pitfall: downloading a “driver pack” from a random site can install bloatware or the wrong driver. Stick to official sources. Also, if you have a PCIe serial card, the driver is usually on the card’s manufacturer site, not the motherboard’s.

When to Consider a Hardware Replacement

If you’ve tried every driver and the device still fails, the hardware may be faulty or incompatible. A cheap PCIe serial card (with a chip like the Oxford or Moschip) will work with Windows built-in drivers in most cases. Before buying, check the card’s chipset and confirm it has Windows 10/11 drivers. This is a practical alternative if the motherboard’s serial port is obsolete or broken.

Frequently Asked Questions

Why does Windows show “PCI Serial Port” instead of a COM port?

Because the driver is missing. Windows only assigns a COM number when it recognizes the device. Once you install the correct driver, it will appear under “Ports (COM & LPT)” with a COM number like COM3 or COM4.

Is it safe to ignore this error?

Yes, if you don’t use any serial devices. The error doesn’t affect other hardware. But if you plan to use a serial device later, you’ll need to fix it then.

Can I use Windows Update to fix it?

Sometimes. Right-click the device and choose “Update driver” → “Search automatically”. If Windows Update has a compatible driver, it will install. It’s worth trying before manual downloads.

What if the hardware ID shows VEN_8086 but Intel’s driver doesn’t work?

Intel’s generic chipset driver may not cover every serial controller. Check your motherboard’s support page for a specific “Serial IO” driver. Also, some Intel controllers are managed by the ME (Management Engine) driver—install that as well.

Do I need to disable driver signature enforcement?

Only if you’re installing an unsigned driver, which is rare for official drivers. If you get a signature error, try a different driver version first. Disabling signature enforcement is a temporary workaround, not a permanent solution.

Will a PCIe serial card fix this without drivers?

Most modern PCIe serial cards use chips that have built-in Windows drivers (like the Moschip MCS9900). You may still need to install the card’s own driver, but it’s usually a simple setup. Check the card’s specifications before buying.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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