Running System File Checker (SFC) is one of the most effective ways to repair corrupted system files in Windows. You can open the command prompt as administrator and run the sfc /scannow command to scan and restore missing system files. However, sometimes you may notice SFC Scannow Not Working, the tool itself displays the error “Windows Resource Protection could not start the repair service.” This error usually means the Windows Modules Installer service (also known as TrustedInstaller), which is required to run System File Checker (SFC) scans, is not working correctly. Let’s take a look at how to troubleshoot this error in a few easy steps.
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Why is SFC Scannow Not Working?
The System File Checker (SFC) utility built into Windows allows users to scan and repair corrupted system files. However, if the SFC scan fails, it could be because the system image is outdated or corrupted, the command is run with insufficient permissions, or other software is interfering.
Well, if it displays error “Windows Resource Protection could not start the repair service,” it usually means the Windows Modules Installer service (also known as TrustedInstaller) is not running or is disabled.
The TrustedInstaller controls the Windows Resource Protection (WRP) tool, which protects against unauthorized modifications, including changes to essential system files, folders, and registry keys. It also handles the “sfc /scannow” command that you’re trying to use. And if, for some reason, the TrustedInstaller service is not started or stuck, it affects both WRP and the System File Checker tool will fail to work properly.
Restart the Windows Modules Installer (TrustedInstaller) Service
SFC needs the TrustedInstaller service to scan and repair Windows system files. If the service is disabled or stuck, SFC cannot run and shows this error.
- Press the Windows key + R, type services.msc, and click ok
- Scroll down to locate Windows Module Installer, right-click on it, and select restart.
- Well, if the service is not started, double-click on the Windows Module installer to open the properties.
- Here, change the startup type to automatic and start the service next to the service status.
- Now click Apply And ok to make Save changes.
Also, you can open the command prompt as administrator and run the following command to start the Windows module installer.
- sc config trustedinstaller start= auto (This will set the Windows Modules Installer service startup type to automatic)
- net start trustedinstaller (restart the TrustedInstaller service:)
Now open the Command prompt as administrator, then type sfc /scannow. Check this time System file checker Start the Scanning process without any error.
Run the SFC scan in Safe Mode
Safe Mode is a diagnostic mode that starts Windows with a minimal set of drivers and services. Also, running the SFC scan in Safe Mode can help to eliminate any issues caused by third-party software or drivers.
Running the SFC scan in Safe Mode is a quick workaround
- Press Windows key + R, type msconfig.msc, and click ok to open the system configuration window
- Move to the boot tab, check the Safe boot option, and select the Minimal option
- Click Apply and OK to save the changes, then restart your PC
- This will start your computer in safe mode, running only essential Windows services.
- Open the command prompt as administrator and run sfc /scannow command.
To disable Safe Boot, launch System Configuration, open the Boot tab, and uncheck Safe Boot under Boot options. Then, click Apply and restart your PC.
Use DISM to Repair Windows Image
If the system image is damaged, SFC cannot repair files. DISM (Deployment Image Servicing and Management) fixes the underlying Windows image so SFC can complete successfully.
Open the command prompt as administrator and run the following command.
DISM /Online /Cleanup-Image /RestoreHealth
The above command scans and patches faulty files in the component store of the Windows system image, allowing SFC to function correctly.
The DISM RestoreHealth command can be useful when the SFC (System File Checker) tool is not able to fix system file issues on its own.
In addition, Malware or virus infections can damage system files and prevent them from functioning correctly. Run a full system scan with your antivirus software to check for any infections.
Install Pending Windows Updates
Windows Updates often include important servicing stack updates, security patches, and system file repairs. If your system is missing a required update or has an incomplete update, the TrustedInstaller service may fail to start properly, causing SFC to show the error.
- Open Settings → Windows Update.
- Click Check for updates.
- Download and install all available updates,
- Once updates finish installing, restart your PC to apply changes.
Installing the latest updates refreshes critical components and restores missing or damaged files that SFC depends on.
Frequently Asked Questions
1. What causes “Windows Resource Protection could not start the repair service”?
Usually, a disabled TrustedInstaller service, corrupted Windows Update components, or system permission issues.
2. How do I enable TrustedInstaller?
Open Services → Windows Modules Installer → set Startup type to Manual or Automatic, then click Start.
3. Why won’t SFC /scannow run?
Because the repair service (TrustedInstaller) is not running or the Windows image is corrupted.
4. Does DISM fix this error?
Yes. DISM repairs the Windows image so SFC can access protected files again.
5. Will a repair install delete my files?
No. A repair install keeps your personal files and apps.
