sfc /scannow: how to run it and fix 'could not repair' errors
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
- Windows 10 or Windows 11. Both
sfcandDISMship with the operating system; runwinverto 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 /scannowworks 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 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.
net sessionExample 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
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.
sfc /scannowWhy: 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:
shutdown /r /t 0Example 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
What to do: run DISM, wait for it to finish, then repeat sfc /scannow and restart.
DISM /Online /Cleanup-Image /RestoreHealthWhy: 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: <build shown by winver>
Image Version: <build shown by winver>
[==========================100.0%==========================]
The restore operation completed successfully.
The operation completed successfully.Then rerun the checker and read the result again:
sfc /scannowSuccess 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:
sfcdoes 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 /RestoreHealthfrom the elevated window with the network connected, then rerunsfc /scannow, thenshutdown /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 rerunsfc /scannow. If it fails the same way again, openC:\Windows\Logs\CBS\CBS.logand 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: 0x800f081ffollowed byThe 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/Sourceoption, 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, and for built-in AI features of the system see Windows with AI: Copilot and neural networks in the system.
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.
🤖 AI summary
- Updated: 2026-11-02
- Topics: sfc, scannow, Windows, DISM, CBS.log, системные файлы
- Summary: Running sfc /scannow step by step: admin prompt, reading CBS.log, when DISM is needed, and why the same errors keep coming back.
- Key facts:
- 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 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.