The issue self corrected this morning and was able to install without using any of the options below.
Latest Security Update KB5079473 (26200.8037) Fails to Install
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(112.00000000000001, 45%, 20%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EDG%3C/text%3E%3C/svg%3E)
Doug Golden
5
Reputation points
Have downloaded and attempted to install multiple times with continued error 0x800f0991. What should I do to fix this problem?
Windows for home | Windows 11 | Windows update
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(115.19999999999999, 60%, 21%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EDK%3C/text%3E%3C/svg%3E)
dilkhush kumar jha 0 Reputation points2026-03-12T18:10:58.81+00:00 I am getting this error Install error - 0x80070002. Not able to install anything and having no brightness control options.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(204.8, 70%, 29%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ESG%3C/text%3E%3C/svg%3E)
Sandra Goulet 15 Reputation points2026-03-12T19:32:12.9133333+00:00 When installing KB507473 I am getting the same error Install error - 0x80070002. I have tried numerous fixes and nothing works. Only having this issue on one machine.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(73.60000000000001, 69%, 17%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EJ%3C/text%3E%3C/svg%3E)
JardaB 0 Reputation points2026-03-12T22:22:34.45+00:00 The KB5079473 update did not complete; it reported a problem, twice returning the system to its previous state and restarting. Fortunately, the system booted up, and the Update indicates a failed update with an offer to repeat.
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David-M 106.8K Reputation points Independent Advisor2026-03-11T12:23:28.9166667+00:00 Hi. I'm David, and I'm happy to help you.
Please clarify the following:
Do you have a third-party antivirus installed? If yes, which one?
Also. What is the current "OS Build" of your Windows 11?
- Press "Windows + R", type
winver, and click OK.
If you prefer, share a screenshot. Use the shortcut "Windows + Shift + S" to use the screenshot tool.
Be sure to censor your email address if it appears. The Microsoft Q&A is public.
I await your reply.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(281.6, 98%, 37%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ESM%3C/text%3E%3C/svg%3E)
Åsmund Møll Frengstad 0 Reputation points2026-03-12T13:27:45.34+00:00 I'm experience the same issue and no external anti virus installed.
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Q&A Assist2026-03-11T11:48:23.19+00:00 AI generated content. This question contains an answer created with AI from Q&A Assist. Learn moreError 0x800f0991 is a Windows Update installation failure. The context only provides supported remediation steps for specific, documented Windows Update errors. For general update failures, use the supported repair and retry paths shown in the documentation:
- Run the Windows image cleanup tool
- Open Start, type
cmd. - Right‑click Command Prompt and select Run as administrator.
- Approve the UAC prompt.
- Run:
dism /online /cleanup-image /startcomponentcleanup - Wait for the command to complete, then restart the device.
- After restart, go to Settings → Windows Update and try installing KB5079473 again.
- Open Start, type
- If the update still fails
- Follow the general guidance in Get help with Windows upgrade and installation errors (linked from the Windows 10 article but applicable as the supported escalation path for Windows Update issues).
- If the failure persists and is specific to a security update (similar to KB5012170 or KB5034765 cases), install the latest Servicing Stack Update (SSU) and latest cumulative update (LCU) for Windows 11, then retry KB5079473. Newer LCUs can contain fixes for prior update installation issues.
If repeated attempts still fail after DISM cleanup and installing the latest SSU/LCU, collect CBS.log and open a support case so Microsoft can analyze the specific 0x800f0991 failure on the device.
References:
- When trying to install updates from Windows Update you might receive "Updates Failed. There were problems installing some updates, but we'll try again later" with Errors: 0x80073701, 0x800f0988
- KB5012170: Security update for Secure Boot DBX
- February 13, 2024—KB5034765 (OS Builds 22621.3155 and 22631.3155)
- Troubleshoot Windows Update installation error 0x800f0831
- Run the Windows image cleanup tool