How to fix
Windows update error 0x800f0991
on Windows

Hey, I can't seem to install the latest Windows updates because of the 0x800f0991 error. Are there any tips you could give me to bypass this error code?

Windows updates are essential for maintaining the health, security, and performance of a Windows-based computer system. Microsoft releases these updates periodically, usually on the second Tuesday of each month, known as "Patch Tuesday." These updates can be categorized into three main types: feature updates that introduce new functionalities, quality updates that improve existing features and address bugs, and security updates that patch vulnerabilities to enhance system protection. The update process is generally automatic, requiring minimal user intervention.

However, the update process doesn't always go smoothly. Users might encounter errors during the update, one of which is the 0x800f0991 error code. This error can disrupt the update process and prevent the system from installing crucial updates. It usually appears during the download or installation phase, and it signifies that the update cannot be completed for some reason.

There are multiple factors that can cause the 0x800f0991 error. One of the most common reasons is disabled essential Windows services such as Windows Update service or Background Intelligent Transfer Service (BITS). These services are integral to the update process, and their malfunction or deactivation could trigger the error.

Another potential cause is corrupted system files. These could be files essential for the Windows Update process or other system files that interact with it. Yet another reason could be issues with the SoftwareDistribution folder, which acts as a cache for Windows Update files. If this folder becomes corrupted or bugged, it can result in the error in question.

There are several methods to resolve the 0x800f0991 error, such as re-enabling essential services, repairing corrupted files, and resetting the SoftwareDistribution folder. Each approach targets a potential cause of the problem, aiming to ensure that the update process can proceed as intended.

For those who prefer an automated way to resolve Windows issues, using a [d1] PC repair tool is highly recommended. This software is designed to identify and fix Windows problems automatically, offering a convenient solution to errors like 0x800f0991.

Fix 1. Run SFC and DISM

System File Checker (SFC) and Deployment Imaging Service and Management Tool (DISM) are built-in utilities that can repair corrupted system files. SFC scans and replaces faulty files, while DISM repairs the Windows image.

• Type cmd in Windows search.
• Right-click on Command Prompt and pick Run as administrator.
• The User Account Control window will ask whether you want to allow changes - click Yes.
• In the Command Prompt window, paste the following command and hit Enter:
  sfc /scannow
• Once the scan is complete, use the following commands and press Enter after each:
  Dism /Online /Cleanup-Image /CheckHealth
  Dism /Online /Cleanup-Image /ScanHealth
  Dism /Online /Cleanup-Image /RestoreHealth
  
• (Note: if you get an error executing this last command, add /Source:C:\RepairSource\Windows /LimitAccess to it and try again).
• Restart your computer.

Fix 2. Use Windows update troubleshooter

Windows Update Troubleshooter is a diagnostic tool that can automatically detect and fix issues that prevent updates from installing.

• Type Troubleshoot in Windows search and hit Enter.
• Select Additional troubleshooters/Other troubleshooters.
• Find Windows Update from the list and select Run the troubleshooter/Run.
• Wait till the scan is finished - you will be provided with potential causes so you can proceed with fixes.
• If no suggestions were provided, proceed with the solutions below.

Fix 3. (Re)start relevant services

Some Windows services like BITS and Windows Update service are crucial for updates. Restarting them can sometimes resolve the issue.

• Type in Services in Windows search and hit Enter.
• Locate Background Intelligent Transfer Service (BITS).
• If this service is already running, right-click and select Restart.
• If it is not running, double-click it, select Automatic under the Startup type from the drop-down menu.
• Click Start, Apply, and OK.
• Repeat the process with the Windows Update, Cryptographic, and Windows Installer services.

Fix 4. Install the update manually

If the automatic update fails, you can download and install the specific update manually from Microsoft's Update Catalog.

• Type in Updates in Windows search and press Enter.
• Select View update history.
• Find the update that failed with the 0x800f0991 error and copy its KB number.
• Open your browser and go to Microsoft Update Catalog.
• Within the search bar, type in the KB number and clicks Search.
• Find the correct version of the update for your operating system (to check this, right-click on Start and pick System. Under Device specifications and check the System type) and click Download.
• Use on-screen guidelines to finish the installation process and restart your system.

Fix 5. Disable third-party security and similar software

Sometimes, third-party security software interferes with the Windows update process. While it's not advisable to keep your security software disabled for an extended period, you may need to turn it off temporarily to allow the update to install. Ensure that you re-enable it once the update is complete.

Fix 6. Reset Windows update components

Resetting the SoftwareDistribution and Catroot2 folders can resolve issues related to corrupted cache.

• Type cmd into Windows search.
• Right-click on Command Prompt and select Run as administrator.
• When User Account Control (UAC) window shows up, click Yes.
• Paste in each of these commands, pressing Enter every time:
  net stop bits
  net stop wuauserv
  net stop appidsvc
  net stop cryptsvc
  Del “%ALLUSERSPROFILE%\Application Data\Microsoft\Network\Downloader\*.*”
  rmdir %systemroot%\SoftwareDistribution /S /Q
  rmdir %systemroot%\system32\catroot2 /S /Q
  regsvr32.exe /s atl.dll
  regsvr32.exe /s urlmon.dll
  regsvr32.exe /s mshtml.dll
  netsh winsock reset
  netsh winsock reset proxy
  net start bits
  net start wuauserv
  net start appidsvc
  net start cryptsvc 
• Restart your device.

Fix 7. Perform Disk Cleanup

Disk Cleanup can help by clearing out temporary files that might be causing issues.

• Open the Windows search bar and type Disk Cleanup. Press Enter to open the Disk Cleanup utility.
• In the Disk Cleanup window, click Clean up system files.
• Select the drive again and click OK.
• In the list of files that can be cleaned up, select the largest portions of data, such as Temporary Internet Files, Windows Update, Temporary Files, and others.
• Click OK to begin the cleanup process.

Fix 8. Use Media Creation Tool to upgrade

If other methods fail, using the Media Creation Tool to perform an in-place upgrade can resolve the issue.

• Visit the official Microsoft website and download Windows 10 installation media (Windows 11 version).
• Double-click the installer and select Yes when UAC shows up.
• Agree to terms.
• Select Upgrade this PC now and click Next.
• Windows will start downloading the needed files.
• Agree to the terms once again and click Next.
• Before installing, make sure that you are happy with your choices (otherwise, you can click Change what to keep option).
• Finally, click Install to begin the upgrade process.