# sfc /scannow: how to run it and fix 'could not repair' errors > AI Release · @ai_release1 · https://ai-release.org/guides/sfc-scannow-kak-zapustit_en.html ## TL;DR - **Time:** about 20 minutes of hands-on work; the scans themselves run unattended and how long they take depends on your disk and on how much is damaged. - **Difficulty:** Basic - **You will need:** a Windows PC, an account in the Administrators group, an elevated Command Prompt or PowerShell window, an internet connection (DISM only), and your BitLocker recovery key if the system drive is encrypted. ## Requirements and setup ![Illustration: Requirements and setup](https://ai-release.org/guides/img/sfc-scannow-kak-zapustit-en-1.jpg?v=1793609557) - **Windows 10 or Windows 11.** Both `sfc` and `DISM` ship with the operating system; run `winver` to see your exact build. The wording of the result lines differs between builds and interface languages — compare the text on your screen with the official documentation for your build. - **Administrator rights.** Both commands write into protected system locations. A normal prompt fails with `Access is denied`. - **Internet access.** Required only for `DISM /Online /Cleanup-Image /RestoreHealth`, which fetches replacement files. `sfc /scannow` works offline because it reads the local component store. - **BitLocker recovery key.** If your drive is encrypted, a repair followed by a reboot may ask for the key before Windows starts. Keep it at hand — see [BitLocker: how to recover your key and avoid losing data](https://ai-release.org/guides/bitlocker-vosstanovlenie-klyucha.html?utm_source=tg&utm_medium=channel&utm_campaign=guide_inline&utm_content=guide_to_guide) before you begin. - **A reboot window.** The last step of a successful repair is a restart, so do not start this five minutes before a meeting. Pre-flight checklist: - [ ] Signed in with an account that belongs to the Administrators group - [ ] Elevated command window open — the title bar starts with `Administrator:` - [ ] Network connection available for the DISM step - [ ] BitLocker recovery key saved somewhere other than the encrypted drive - [ ] Open documents saved and other maintenance tools closed ## Step 1. Open an elevated Command Prompt and confirm the rights **What to do:** press `Win + X` and pick **Terminal (Admin)** on Windows 11 or **Windows PowerShell (Admin)** on Windows 10, then confirm the User Account Control prompt with **Yes**. On older builds, press `Start`, type `cmd`, right-click **Command Prompt** and choose **Run as administrator**. **Why:** both repair tools modify protected system files. Started from a normal window, they can read but not repair, and you waste a full scan before seeing `Access is denied`. **How to check:** run `net session`. An elevated window answers with an empty session list; a normal one returns error 5. ```powershell net session ``` Example of a correctly elevated window: ``` C:\Windows\system32>net session There are no entries in the list. ``` Example of a window that is **not** elevated — stop here and reopen it as administrator: ``` System error 5 has occurred. Access is denied. ``` ## Step 2. Run sfc /scannow and read the result line ![Illustration: Step 2. Run sfc /scannow and read the result line](https://ai-release.org/guides/img/sfc-scannow-kak-zapustit-en-2.jpg?v=1793609560) **What to do:** type the command below and press Enter. Leave the window open and do not close it while the verification percentage is moving. ```powershell sfc /scannow ``` **Why:** SFC (System File Checker) is the Windows tool that checks every protected system file against its known-good copy and replaces damaged ones from the local component store. It is the first step because it repairs most corruption locally, without a network connection. **How to check:** the last line of output tells you which branch you are on. Match it against this table. | Line on screen | What it means | Next action | |---|---|---| | `Windows Resource Protection did not find any integrity violations.` | No damaged system files | Nothing to repair — go to Step 3 to confirm | | `Windows Resource Protection found corrupt files and successfully repaired them.` | Files were replaced | Restart the PC, then re-check | | `Windows Resource Protection found corrupt files but was unable to fix some of them.` | The source of the good copies is damaged | Go to Step 3 (DISM) | | `Windows Resource Protection could not perform the requested operation.` | The scan was interrupted or blocked | See Troubleshooting | If the scan repaired files, restart immediately so the replaced binaries are loaded: ```powershell shutdown /r /t 0 ``` Example of the fully repaired branch on screen: ``` Beginning verification phase of system scan. Verification 100% complete. Windows Resource Protection found corrupt files and successfully repaired them. ``` ## Step 3. Repair the component store with DISM, then verify ![Illustration: Step 3. Repair the component store with DISM, then verify](https://ai-release.org/guides/img/sfc-scannow-kak-zapustit-en-3.jpg?v=1793609565) **What to do:** run DISM, wait for it to finish, then repeat `sfc /scannow` and restart. ```powershell DISM /Online /Cleanup-Image /RestoreHealth ``` **Why:** DISM (Deployment Image Servicing and Management) rebuilds the system image — the component store — from which `sfc` takes its original files. That is why the two commands are used as a pair: `sfc` fixes the live system, DISM fixes the source `sfc` copies from. `/Online` targets the running installation and `/RestoreHealth` performs the repair; the command needs administrator rights and an internet connection. **How to check:** the tool prints its progress and then a completion line. Example: ``` Deployment Image Servicing and Management tool Version: Image Version: [==========================100.0%==========================] The restore operation completed successfully. The operation completed successfully. ``` Then rerun the checker and read the result again: ```powershell sfc /scannow ``` Success looks like either `Windows Resource Protection did not find any integrity violations.` or `Windows Resource Protection found corrupt files and successfully repaired them.` Restart the PC. The final confirmation is behavioural: the original symptom (random crashes, a broken Start menu, features that refuse to open) is gone after the restart. If the symptom survives a clean scan, the cause is outside the system-file layer — check the official documentation for the next diagnostic step rather than repeating the same command. ## Troubleshooting **Problem. SFC finishes, finds damage, and admits it could not repair it.** - Error: `Windows Resource Protection found corrupt files but was unable to fix some of them.` - Cause: `sfc` does not download anything — it copies from the local component store. If that store is damaged as well, there is no good copy to restore from. - Solution: run `DISM /Online /Cleanup-Image /RestoreHealth` from the elevated window with the network connected, then rerun `sfc /scannow`, then `shutdown /r /t 0`. **Problem. The scan dies immediately instead of running.** - Error: `Windows Resource Protection could not perform the requested operation.` - Cause: the scan was interrupted — the window was closed, the machine restarted mid-scan, another servicing operation was still running, or the prompt was not elevated. - Solution: close other maintenance tools, restart the PC, reopen the window as administrator (verify with `net session`), and rerun `sfc /scannow`. If it fails the same way again, open `C:\Windows\Logs\CBS\CBS.log` and read the first error entry of the newest scan block; if the cause is not obvious there, check the documentation for your build. **Problem. DISM stops with an error instead of repairing.** - Error: `Error: 0x800f081f` followed by `The source files could not be found.` - Cause: no working internet connection, a proxy or firewall blocking the download, or damage that the online repair cannot cover. - Solution: test the connection (`ping -n 2 www.microsoft.com`), disable the proxy for the session or allow the tool through the firewall, and rerun the DISM command. If the same error returns, check the official documentation for the `/Source` option, which points DISM at files from installation media instead of the network. ## Summary and next steps Run `sfc /scannow` from an elevated prompt, reboot if it repaired files, and fall back to `DISM /Online /Cleanup-Image /RestoreHealth` plus a second `sfc /scannow` when it reports that it could not fix everything. If repairs or a reinstall disturb your licence, see [Windows 11 activation lost: causes and how to restore your license](https://ai-release.org/guides/sletela-aktivatsiya-windows-11.html?utm_source=tg&utm_medium=channel&utm_campaign=guide_inline&utm_content=guide_to_guide), and for built-in AI features of the system see [Windows with AI: Copilot and neural networks in the system](https://ai-release.org/guides/windows-i-ii.html?utm_source=tg&utm_medium=channel&utm_campaign=guide_inline&utm_content=guide_to_guide). ## FAQ **Does `sfc /scannow` need an internet connection?** No. It compares protected system files against copies already stored on your drive. Only the DISM repair step downloads anything. **Which comes first, SFC or DISM?** Start with `sfc /scannow`. Only when it reports that it was unable to fix files do you run `DISM /Online /Cleanup-Image /RestoreHealth`, and after that you repeat `sfc /scannow` — that order is what makes the pair work. **Do I have to reboot after the scan?** Yes, if `sfc` repaired anything: the replaced files are loaded only after a restart. If it found no violations, no reboot is required for the scan itself. **Can I run these commands on Windows 10 as well as Windows 11?** Both tools are part of the standard Windows servicing stack and are invoked with the same syntax; the exact text of the result lines varies by build and language, so verify the wording against the documentation for your version.