Stop 0x45F IRQ Busy: The Real Fix for IRQ Sharing Conflicts

What actually causes ERROR_IRQ_BUSY (0x0000045F)

This error pops up when Windows tries to open a device driver and the hardware interrupt request (IRQ) line that device is mapped to is already claimed by something else. What's happening here is the motherboard's BIOS or the ACPI subsystem assigned the same IRQ to two or more devices that don't support sharing. Back in the ISA/PnP days this was routine, but with PCI and PCIe it's less common—though some real-world scenarios still trigger it.

I've seen this most often with:

• A sound card sharing an IRQ with a network adapter (especially older Creative or Realtek cards).
• A legacy serial or parallel port conflicting with a USB controller.
• A PCIe slot that's electrically identical to another slot sharing the same IRQ line on the chipset.

Fix 1: Physically move the PCIe card to a different slot

This is the most common fix and the one I'd try first. The reason this works is motherboard manufacturers often wire certain PCIe slots to different interrupt lines—moving a card to a slot that's on a separate IRQ line solves the sharing problem instantly.

1. Shut down the PC completely, unplug the power cord.
2. Open the case and identify which PCIe slot the problematic device is in (look at the error message for device name).
3. Move it to a slot physically further from the CPU. The top x16 slot is often shared with other components, while the bottom x1 or x4 slots are on separate IRQs.
4. Boot into Windows and check Device Manager (devmgmt.msc) for warning icons.

If the error disappears, you're done. If not, the card is likely in a slot that's hardwired to share IRQs with something else on that motherboard. You may need to swap slots with another card that can share IRQs (like a modern GPU that supports MSI-X).

Fix 2: Disable ACPI IRQ arbitration in the BIOS

If moving slots didn't work, the next step is to tell the BIOS to stop mucking with IRQ assignments. This is the nuclear option because it breaks ACPI power management for the PCI subsystem, but it often clears 0x45F on older motherboards (pre-2015) or systems with legacy PCI slots.

1. Reboot and enter BIOS setup (usually F2, Del, or F10 depending on motherboard).
2. Look for ACPI IRQ Arbitration or IRQ Sharing or PCI IRQ Steering. It's often under Advanced → PCI Subsystem Settings or Power Management.
3. Set it to Disabled. If the option doesn't exist, look for PnP/PCI Configurations → IRQ Resources → set to Manual and assign specific IRQs to devices.
4. Save and reboot.

What this does is force the BIOS to use static IRQ assignments instead of letting ACPI re-map them dynamically. The downside: your PC might not enter deep sleep states correctly. But if you're hitting 0x45F, you're probably okay with that trade-off.

Fix 3: Disable the conflicting device in Device Manager

If you can figure out which device is stealing the IRQ, you can simply disable it. This is a hack, not a fix, but it works when you need the PC running now and can't swap hardware.

1. Open Device Manager (Win + X → Device Manager).
2. Click View → Resources by type.
3. Expand Interrupt request (IRQ). Look for the IRQ number that shows multiple devices listed. The 0x45F error message usually includes the failed device—the other one listed on the same IRQ is the culprit.
4. Right-click that other device and choose Disable device. Confirm.
5. Reboot.

This stops the driver for the conflicting device from loading, freeing the IRQ. You lose the functionality of that device, but the error goes away.

Fix 4: Force PCI IRQ steering to a specific range (advanced)

On Windows 10/11 systems with legacy PCI devices (like some Wi-Fi cards or modems), you can use the registry to restrict which IRQs the PCI bus can use. This prevents the driver from trying to use an IRQ that's already occupied.

1. Press Win + R, type regedit, press Enter.
2. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PCI\Parameters
3. If the Parameters key doesn't exist, right-click PCI → New → Key and name it Parameters.
4. Inside Parameters, create a new DWORD (32-bit) value named MaxIRQNumber.
5. Set its value to 15 (decimal). This tells the PCI bus to only use IRQs 0–15, avoiding conflicts with ACPI's higher IRQ range.
6. Also create MinIRQNumber and set it to 3 (decimal) if you want to avoid IRQ 0, 1, 2 (timer, keyboard, etc.).
7. Restart the PC.

The reason this works: PCI devices normally can use IRQs 16–23 (on ACPI systems), but some older drivers assume they'll only get IRQs 0–15 and crash when they get a higher one. Limiting the range forces the device to use an IRQ it can share properly.

Fix 5: Update the chipset driver and BIOS

Believe it or not, I've seen 0x45F resolved by a simple chipset driver update. Modern AMD chipsets (like X570, B650) had a bug in early firmware revisions where PCIe slot IRQs weren't mapped correctly. Same story on Intel Z390 boards from 2018–2019.

1. Identify your motherboard model (run msinfo32 and look for BaseBoard Manufacturer/Product).
2. Download the latest chipset driver from the motherboard vendor's site—not from Windows Update, which is often outdated.
3. Also check BIOS version. If it's more than 12 months old, consider flashing the latest BIOS.
4. Install chipset driver, reboot, then flash BIOS if needed (follow your motherboard manual exactly).

This doesn't always help, but when it does it's because the newer firmware re-maps IRQ assignments to avoid known conflicts.

Quick-reference summary

Start with moving the card. It's free, takes five minutes, and fixes most cases. If that doesn't work and you're on a desktop, the BIOS disable is your next best bet. Laptops? You're stuck with Fix 3 or Fix 4, because you can't move hardware.