SFC /scannow: Fix Corrupted Windows Files

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Black and yellow shield icon illustration representing Windows system file repair with SFC and DISM tools

Last updated: September 17, 2026

If Windows 11 or Windows 10 is showing system errors, crashing, freezing, or behaving strangely, corrupted system files may be part of the problem. One of the most useful built-in repair tools for this is SFC / Scannow.

SFC stands for System File Checker. It scans protected Windows system files, compares them against a known-good version stored by Windows, and attempts to repair any file that has been damaged, altered, or deleted.

This guide explains how to run the SFC command correctly, how to read the scan results, when to bring in DISM, what to do if SFC still cannot repair the files, and which other tools to use when the problem turns out not to be a system-file issue at all.

Quick Answer

To check and repair Windows system files, open Command Prompt as administrator and run:

sfc /scannow

Wait until the scan reaches 100% and read the result.

If SFC says it found corrupted files but could not repair some of them, run:

DISM /Online /Cleanup-Image /RestoreHealth

After DISM finishes, run sfc /scannow again.

Table of Contents

What Is SFC/Scannow?

SFC /scannow is a built-in Windows repair command. SFC stands for System File Checker, a tool that has shipped with Windows since Windows 98 and is still part of Windows 11 and Windows 10 today.

The System File Checker checks protected Windows system files for corruption. When it finds a damaged file, Windows attempts to replace it with a correct copy from a protected cache or from the Windows component store.

The main SFC command is:

sfc /scannow

The /scannow option tells SFC to scan all protected system files immediately and attempt to repair any problems it finds. SFC is mainly intended for Windows system file problems—it does not repair every type of Windows issue, such as problems caused by faulty drivers, failing hardware, or third-party software.

Why Do System Files Get Corrupted?

System files rarely become corrupted on their own. Understanding the common causes can help you avoid repeating the problem after the repair.

  • Sudden power loss or a forced shutdown while Windows is writing to disk.
  • Interrupted Windows updates that stop partway through installation.
  • Failing storage hardware, such as a hard drive or SSD, developing bad sectors.
  • Malware infections that modify or delete protected files.
  • Third-party "cleaner" tools that delete files Windows still needs.
  • Manual deletion or editing of system files by a user or a faulty script.

Knowing the likely cause also helps you decide which tool to reach for. A single bad shutdown usually calls for SFC alone, while failing hardware calls for CHKDSK or a drive health check as well.

When Should You Use SFC/Scannow?

You can use SFC when Windows starts behaving differently from normal, and you suspect that system files may be damaged.

Common situations include:

  • Windows system errors
  • Repeated Windows error messages
  • Unexpected crashes
  • Windows features that stop working correctly
  • Applications affected by damaged Windows files
  • System instability after a software change
  • Problems that appear after a Windows update
  • Windows reporting corrupted or damaged system files

SFC can therefore be an important part of a wider Windows repair process, and it is usually the first tool worth trying because it is fast, safe, and built into Windows.

Before Running SFC

Save your work before starting the scan and close any applications you do not need.

You must open Command Prompt with administrator privileges. A normal Command Prompt window does not have the permissions required to perform the repair, and SFC will refuse to run without them.

If Windows is currently unstable, restart the computer before running the scan—a fresh restart clears any locked files that might interfere with the check.

How to Run SFC / Scannow in Windows 11 and Windows 10

Running sfc /scannow in an administrator Command Prompt window

Step 1: Open Command Prompt as Administrator

Click Start and type:

Command Prompt

Right-click Command Prompt and select Run as administrator.

If User Account Control asks for permission, select Yes.

Step 2: Run the SFC Command

Enter the following command:

sfc /scannow

Press Enter.

Step 3: Let the Scan Finish

SFC will start checking protected Windows system files.

SFC scan progress reaching 100 percent verification

The verification percentage will increase as the scan progresses. Do not close the Command Prompt window while the scan is running, and do not shut down or restart the computer.

Allow the process to reach 100%. The scan may take anywhere from a few minutes to around twenty minutes, depending on the computer and the condition of Windows.

Step 4: Read the Result

When the scan finishes, Windows displays a message describing the result. Read this message carefully before deciding what to do next—it tells you exactly which of the four outcomes below applies.

SFC /scannow Results Explained

Windows Resource Protection did not find any integrity violations.

SFC did not find any corrupted protected system files. If you still have a problem, the cause is likely something other than protected Windows system files—for example, a driver, an application, or a hardware issue.

Windows Resource Protection found corrupt files and successfully repaired them.

SFC found corrupted system files and successfully repaired them. Restart Windows and check whether the original problem has been resolved.

Windows Resource Protection found corrupt files but was unable to fix some of them.

SFC found damaged files but could not repair all of them. This is the clearest sign that you should move on to DISM. After DISM completes, run SFC again.

Windows Resource Protection could not perform the requested operation.

SFC could not complete the requested scan at all. Restart Windows and try again. If the problem continues, try running SFC in Safe Mode.

Run DISM Before SFC

DISM Online Cleanup-Image RestoreHealth command running in Command Prompt

If SFC cannot repair some corrupted files, use the Deployment Image Servicing and Management tool, known as DISM.

SFC repairs files using a local copy stored by Windows. If that local copy is itself damaged, SFC has nothing good to copy from, and the repair fails. DISM fixes this by repairing the underlying Windows component store, which SFC relies on.

Open Command Prompt as administrator and run:

DISM /Online /Cleanup-Image /RestoreHealth

Press Enter and allow the process to finish. This step needs an active internet connection, since DISM may download replacement files directly from Windows Update.

Do not close the Command Prompt while DISM is working, even if the progress bar appears to pause—this is normal and can happen more than once during the process.

Run SFC Again After DISM

Open an administrator Command Prompt if it is not already open and run:

sfc /scannow

Press Enter and wait until the scan reaches 100%.

Running SFC again after DISM gives the System File Checker a working local source to repair from, so it now has another opportunity to fix files that could not be repaired during the first scan.

If SFC successfully repairs the files this time, restart Windows and test the computer.

What If SFC Cannot Complete?

If the SFC scan stops, fails, or reports that it cannot perform the requested operation, work through these steps in order:

  1. Restart the computer.
  2. Open Command Prompt as administrator.
  3. Run the DISM repair command.
  4. Run sfc /scannow again.
  5. Run SFC in Safe Mode if the normal Windows environment still prevents the scan.
  6. Use Windows Recovery options if Windows remains damaged or cannot start normally.

The next two sections explain these last two options in more detail.

Run SFC in Safe Mode.

Command Prompt opened in Windows Safe Mode

If SFC cannot complete while Windows is running normally, Safe Mode is another option worth trying.

Safe Mode starts Windows with a limited set of drivers and services. This can help when a third-party program, driver, or background service is locking a file that SFC needs to replace.

How Safe Mode Can Help

In normal Windows, many programs and services start automatically, and a problem with one of them can sometimes interfere with repair tools. Safe Mode loads a much smaller set of components, giving you a simpler environment in which to try the SFC scan again.

Run SFC in Safe Mode.

First, start Windows in Safe Mode. Then open Command Prompt as administrator and run:

sfc /scannow

Allow the scan to reach 100% and read the final result.

If you need detailed instructions for entering Safe Mode, see our guide:

How to Boot in Safe Mode on Windows 10

After completing the repair, restart the computer normally and check whether Windows is working correctly.

When to Use CHKDSK

CHKDSK has a different purpose from SFC.

SFC checks protected Windows system files. CHKDSK checks the file system and can identify problems with the storage drive and file system structure, such as bad sectors or a corrupted file table.

If you are experiencing file-system errors, drive errors, problems accessing files, or other symptoms that point to the storage device rather than Windows itself, CHKDSK may be more appropriate than SFC.

For example:

chkdsk C: /scan

Do not assume every corrupted file is caused by a damaged drive. SFC and CHKDSK address different types of problems, and running both is a reasonable step if you are not sure which one applies.

Other Windows Repair Options

SFC and DISM are useful Windows repair tools, but some problems require a different approach entirely.

Windows Update

If the problem started right after a Windows update, check Windows Update and investigate whether the update itself is related to the problem.

If Windows Update is not working correctly, see:

Windows 11 Update Not Working? 14 Ways to Fix It

Recent Windows Update Problems

If you are troubleshooting problems tied to a specific Windows update, it helps to check the known issues associated with that update.

For example:

Windows 11 KB5121003 Problems and Fixes

Use Windows Recovery Options.

If SFC and DISM do not solve the problem, or if Windows cannot start normally, you may need the Windows Recovery Environment.

Windows Recovery provides several tools for troubleshooting serious startup and system problems. Available options can vary depending on the condition of the Windows installation.

Startup Repair

Startup Repair is designed to help with certain problems that prevent Windows from starting correctly, and it can be useful when Windows repeatedly fails during startup and you cannot reach the normal desktop.

System Restore

System Restore can return system files, drivers, settings, and installed programs to an earlier restore point, when one is available. This is useful when a recent system change caused the problem.

Uninstall Recent Updates

If a Windows problem began immediately after an update, Windows Recovery may offer an option to uninstall that update, which can resolve issues tied directly to it.

Reset This PC

Reset this PC is a more significant recovery option. It can reinstall Windows and may let you keep personal files depending on the option you choose. Because resetting Windows can affect installed applications and settings, it should not be the first choice when a simpler repair method can solve the problem.

When Windows Keeps Entering Automatic Repair

If Windows repeatedly enters Automatic Repair instead of starting normally, the problem may need a different troubleshooting process. See:

How to Fix the Windows 10 Automatic Repair Loop

This is particularly useful when you cannot stay in normal Windows long enough to complete the usual SFC troubleshooting steps.

How to Check the SFC Log

SFC records information about its scan in the Windows CBS log. If SFC reports that it could not repair some files, this log can tell you exactly which files were involved.

For advanced troubleshooting, run the following command in an administrator Command Prompt:

findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log > "%userprofile%\Desktop\sfcdetails.txt"

This creates a file named sfcdetails.txt on the desktop, listing SFC-related log entries. It can help you identify which specific files could not be repaired, which is useful if you plan to replace a file manually or ask for advanced help.

How to Fix Corrupted Files in Windows 11 and Windows 10

If you are looking for a way to fix corrupted files in Windows 11 or Windows 10, SFC is one of the first built-in tools to try when the corrupted files are protected Windows system files.

A practical repair sequence is

  1. Run SFC /scannow.

    Start by checking the protected Windows system files and let SFC repair whatever it can fix on its own.

  2. Run DISM if SFC cannot repair some files.

    Use DISM /Online /Cleanup-Image /RestoreHealth and wait for it to finish completely.

  3. Run SFC /scannow again.

    After DISM finishes, run SFC again and check the new result.

  4. Use CHKDSK when the problem points to the file system or storage drive.

    SFC and CHKDSK repair different types of problems.

  5. Run SFC in Safe Mode.

    If normal Windows prevents the scan from completing, Safe Mode provides a simpler environment for troubleshooting.

  6. Use Windows Recovery options.

    If Windows remains seriously damaged or cannot start normally, recovery tools such as Startup Repair, System Restore, or update removal may be needed.

This sequence covers most common situations involving corrupted Windows system files. The correct repair depends on the actual cause of the problem, so work through the steps in order rather than skipping ahead.

If the problem began after a Windows update, investigate the update as well—corrupted system files may be a symptom rather than the only cause. For Windows 11 update troubleshooting, see:

Windows 11 Update Not Working? 14 Ways to Fix It

Frequently Asked Questions

What does SFC/Scannow do?

SFC /scannow checks protected Windows system files and attempts to repair damaged or corrupted files.

Is SFC /scannow available in Windows 11?

Yes. SFC /scannow is available in both Windows 11 and Windows 10.

Should I run DISM before SFC?

If SFC cannot repair corrupted files, run DISM first and then run SFC again.

How long does SFC/Scannow take?

The time varies between computers, typically a few minutes to about twenty minutes. Allow the scan to finish completely instead of stopping it because it appears to take a long time.

Can SFC fix all Windows problems?

No. SFC is mainly designed to check protected Windows system files. Problems involving drivers, applications, hardware, storage, Windows updates, or user profiles may require other solutions.

What should I do if SFC cannot repair corrupted files?

Run DISM, allow it to finish, and then run sfc /scannow again. If the problem continues, try Safe Mode or an appropriate Windows Recovery option.

Can I run SFC in Safe Mode?

Yes. If SFC cannot complete in normal Windows, you can try running the command in Safe Mode.

What is the difference between SFC and CHKDSK?

SFC checks protected Windows system files. CHKDSK checks the file system and storage-related errors. They are designed for different types of problems.

What can I do if Windows cannot start normally?

If Windows cannot start normally, use Windows Recovery options such as Startup Repair, System Restore, or other available recovery tools. Safe Mode may also be useful when it is available.

Does SFC /scannow delete any files?

No. SFC only checks and repairs protected system files. It does not delete personal files, documents, photos, or installed applications.

Quick Windows Repair Checklist

  • ☐ Save your work and close unnecessary applications.
  • ☐ Open Command Prompt as administrator.
  • ☐ Run sfc /scannow.
  • ☐ Wait for the scan to reach 100%.
  • ☐ Read the SFC result.
  • ☐ Run DISM if SFC cannot repair all corrupted files.
  • ☐ Run SFC again after DISM.
  • ☐ Use CHKDSK when the problem points to the file system or drive.
  • ☐ Run SFC in Safe Mode if the normal scan cannot complete.
  • ☐ Use Windows Recovery options for serious startup or system problems.
  • ☐ Restart Windows and test the original problem after repairs.

Conclusion

SFC /scannow is one of the most useful built-in Windows repair commands. It checks protected system files and repairs many corrupted Windows files without installing any additional software.

A common repair sequence is to start with SFC. If SFC cannot repair some files, run DISM and then run SFC again. If SFC still cannot complete in normal Windows, try Safe Mode. If Windows remains seriously damaged or cannot start normally, Windows Recovery options may be necessary.

SFC is only one part of Windows troubleshooting. If the problem involves the storage drive, Windows Update, drivers, startup, applications, or hardware, use the repair method that matches the actual problem.

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