Fix Windows Defender Engine Unavailable Error (Solved!)

Methods to solve Windows Defender Engine Unavailable Error.

Windows Defender Engine Unavailable

Windows Security has a tool called Virus & threat protection which helps you run different types of scanning but several users complain about an unpleasant situation with this. In the Security at a glance page, this setting displays Engine available error. As a result, you can not run scanning and manage settings. If you face this issue on your system, then please read this article for the causes and resolutions.

The main causes behind this problem are inconsistent services, corrupt Windows Defender files, damaged system files, and an interfering third-party anti-virus. Furthermore, outdated definition update, incorrect registry, and broken Windows Security app might trigger this issue. See: Fix Windows Defender Update Stuck in Windows 10. Now to resolve this, you can try the following solutions:

Windows Defender Engine Unavailable

Here is how to fix Windows Defender Engine Unavailable Error –

Manually install Windows Defender

Microsoft provides “Microsoft Defender Antivirus” for Windows 11, Windows 10, and other versions to manually install the application. This may solve the Windows Defender unavailable error so follow the guide:

  1. Navigate to this page.
  2. Scroll down and click on the correct link for “Microsoft Defender Antivirus for Windows 11, Windows 10, Windows 8.1, and Windows Server”.
how to fix Windows Defender Engine Unavailable Error
  1. Double-click on mpam-fe.exe from the Downloads folder to install the app.

Restart the Security Center service

The Security Center service manages the Windows Defender process. If this service is stopped, you will encounter the “Windows Defender Engine Unavailable” error. To resolve this problem, you can consider restarting this service using the below steps:

  1. Type Services in the Windows Search bar and press Enter.
  2. Click on the application to open it.
  3. Scroll down to the Security Center service.
  4. Right-click on the Security Center.
  5. Select Restart.

Use System File Checker

If the service associated with Windows Defender is restarted and you are sure that it is running and the error still occurs, then it is quite possible that the system files are corrupt. In this case, you can try running the SFC Scan. Scan by this utility can check for missing and corrupt files on the system and repair them if possible.

  1. Click on Search and type Command Prompt.
  2. Select Run as administrator in the right panel.
  3. Once the elevated Command Prompt window appears, type the below command and press Enter:


Use System File Checker through cmd command line sfc /scannow
  1. The tool will scan for all the files; when it completes 100%, restart your system.

Change Registry Entry

Windows Defender can cease to work if modifications are made to the Registry Editor window. These changes can be pushed through third-party software or a recent Windows Update. In this case, you can fix the Registry value:

  1. Press Windows + R.
  2. In the Run window, type the command REGEDIT and hit Enter.
  3. In the Registry Editor, navigate to the following path:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
  1. You will notice a DWORD 32-bit entry named DisableAntiSpyware in the right panel.
  2. Double-click on the Entry to open its properties.
  3. Change the value of the Value Data to 0.
  4. Click on OK to save the settings.
  5. Repeat the procedure for the DisableAntiVirus DWORD 32-bit Entry on the same window.
  6. Reboot your system.

Update Windows to the latest version

Windows Defender engine unavailable error occurs if the latest security updates are not installed on your system. While Windows automatically pushes updates if they were deferred, you can update Windows manually.

  1. Right-click on the Start and select Settings.
  2. Select Windows Update on the left panel.
  3. In the right pane, click on Check for updates.
  4. Reboot the system once the updates have been completed.

Install the latest Definition update

Windows Defender receives definition updates at regular intervals to cover the latest threats. Attackers often create programs with new modules to penetrate the Computer security and execute this remotely.

Microsoft develops the definition updates accordingly to scan and neutralize the threats. You can install this using the Windows Security app with the steps as follows:

  1. Click on Start and type security.
  2. Select “Windows Security” App.
  3. Then, click on Virus & threat protection.
  4. Select the link Protection updates.
  5. Now click on Check for updates.
fix Windows Defender Engine Unavailable

Read: Everything You Can Do in Windows Defender Security Center on Windows 11 or 10.

Uninstall third-party antivirus program

Due to interference with third-party antivirus programs, Windows Defender engine unavailable error might appear in Virus & threat protection. These might be Malwarebytes, Kaspersky, or other that prevent the Windows Defender from working properly.  But you can uninstall them easily:

  1. Press Windows key and type appwiz.cpl.
  2. When Programs and Features window opens, find the antivirus.
  3. Right click on that program and select Uninstall.
  4. If a confirmation prompt appears, click on Yes.
  5. In case, Uninstallation wizard opens, follow the onscreen instructions.
  6. Restart your computer and see Windows Security app.

Reset the Windows Security application

Windows 11 and 10 provide options to reset any built-in app including Windows Security app and this will restore the default settings. If the error appears because of glitches in Settings then this process will help you. Therefore, move forward with the steps:

  1. Right-click on Start and select Settings.
  2. Click on Apps from the left pane.
  3. Select Installed apps.
  4. Once the new page is loaded completely, find Windows Security.
  5. Click on 3 dots icon for the app and select Advanced options.
  6. From the new page, click on Reset.
reset the Windows Security app from settings
  1. On the popup, again click on “Reset”.
  2. Now launch the Windows Security app and go to Virus & threat protection.
  3. See if Engine not available message is gone.

If you want to reset the app using cmdlet then:

  1. Click on Start and type PowerShell.
  2. Select – Run as administrator.
  3. On User account control, click on Yes.
  4. On the Windows PowerShell, type the following cmdlet and press Enter:
Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage
  1. Start Windows Security.

Manually install Windows Defender
Restart the Security Center service
Use System File Checker
Change Registry Entry
Update Windows to the latest version
Install the latest Definition update
Uninstall third-party antivirus program
Reset the Windows Security application

That’s all!!

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Topics:  Windows
About Karan Khanna
Karan is a B.Tech graduate and a technology enthusiast. He has worked towards Windows troubleshooting since 2013.