Fixing Windows Defender Antivirus Scan Not Working: A Troubleshooting Guide

Microsoft Defender Antivirus is designed to run silently in the background, proactively safeguarding your system by scanning files and processes in real-time. This essential security measure ensures that potential malware threats are identified and neutralized before they can compromise your device. However, you might encounter situations where Windows Defender Antivirus scan is not functioning as expected. This can leave your system vulnerable and requires immediate attention.

This guide provides comprehensive troubleshooting steps to address the issue of Windows Defender Antivirus scan not working, ensuring your system remains protected.

Identifying and Resolving Scan Issues in Windows Defender

When your Windows Defender scan is not working, it can manifest in various ways. You might notice that scans are not initiating, getting stuck midway, displaying errors, or simply not detecting threats as expected. Here’s a structured approach to diagnose and fix these problems:

1. Check Windows Defender Service Status

The core functionality of Windows Defender Antivirus relies on its services running correctly in the background. If these services are disabled or not functioning properly, scanning will be impaired.

How to check and start Windows Defender services:

1. Press Windows Key + R, type services.msc, and press Enter to open the Services window.
2. Scroll down and locate the following services:
   • Microsoft Defender Antivirus Service
   • Microsoft Defender Antivirus Network Inspection Service
3. For each service, check the Status column:
   • If the status is Stopped or Disabled, right-click on the service and select Properties.
   • In the Startup type dropdown, choose Automatic.
   • Click Start to initiate the service.
   • Click Apply and then OK.

Restart your computer after ensuring these services are running and check if the scan function is restored.

2. Restart the Windows Security Service

Sometimes, a simple restart of the Windows Security service, which manages Windows Defender, can resolve temporary glitches that might be preventing scans.

Steps to restart Windows Security Service:

1. Open the Services window again (as described in step 1 above).
2. Locate the Security Center service (it might also be named wscsvc in the service list).
3. Right-click on Security Center and select Restart.

After restarting the service, attempt to run a scan to see if the issue persists.

3. Run System File Checker (SFC) Scan

Corrupted system files can lead to various malfunctions, including issues with Windows Defender. The System File Checker (SFC) is a built-in tool that scans for and repairs corrupted system files.

How to run SFC Scan:

1. Open Command Prompt as Administrator:
   • Press Windows Key, type cmd, right-click on Command Prompt, and select Run as administrator.
2. In the Command Prompt window, type sfc /scannow and press Enter.
3. Wait for the scan to complete. This process may take some time.
4. If SFC finds and repairs any corrupted files, restart your computer.

After the restart, check if Windows Defender scan is now working correctly.

4. Check for Malware Conflicts

In some cases, existing malware on your system might be interfering with Windows Defender’s ability to scan or function properly. Running a scan with a reputable third-party malware removal tool can help identify and eliminate such conflicts.

Using a Malware Removal Tool:

Consider using tools like Malwarebytes or HitmanPro to perform a thorough scan of your system. These tools can sometimes detect and remove malware that might be hindering Windows Defender. Remember to run these tools in safe mode for a more effective scan.

5. Update Windows Defender Antivirus Definitions

Outdated virus definitions can sometimes cause scanning irregularities. Ensuring that Windows Defender has the latest definitions is crucial for effective threat detection and proper functioning.

Updating Windows Defender Definitions:

1. Open Windows Security by clicking the shield icon in the system tray or searching for “Windows Security” in the Start Menu.
2. Click on Virus & threat protection.
3. Under Virus & threat protection updates, click on Check for updates.

Alt text: Windows Security interface showing Virus & threat protection updates section, highlighting the ‘Check for updates’ button.

Ensure your definitions are up to date and then test the scan functionality.

6. Check for Conflicting Security Software

Having multiple antivirus programs installed on your system can lead to conflicts, often disabling or impairing the functionality of one or both. If you have recently installed another antivirus program, it might be interfering with Windows Defender.

Resolving Software Conflicts:

Uninstall any other antivirus software that might be installed on your system. After uninstalling, restart your computer and check if Windows Defender scan starts working. Windows typically enables Defender automatically when it detects no other active antivirus is present.

7. Review Windows Defender Exclusions (Briefly)

While less likely to be the primary cause of a completely non-functional scan, it’s worth quickly checking if any overly broad exclusions have been accidentally set up in Windows Defender, though the original article is about exclusions, in this context we are checking if exclusions are mistakenly causing issues.

Checking Exclusions:

1. Open Windows Security.
2. Click on Virus & threat protection.
3. Under Virus & threat protection settings, click on Manage settings.
4. Scroll down to Exclusions and click on Add or remove exclusions.
5. Review the list of exclusions. If you find any entries that seem suspicious or unintentionally broad, remove them.

Alt text: Windows Security settings interface showing Virus & threat protection settings with Exclusions option highlighted.

Caution: Avoid adding unnecessary exclusions as they can reduce your system’s security. Exclusions should only be added if you have a specific, well-justified reason, like for certain developer tools or files you know are safe.

8. Run the Windows Troubleshooter

Windows includes built-in troubleshooters that can automatically diagnose and fix various system problems, including issues with security components.

Using the Troubleshooter:

1. Open Settings by pressing Windows Key + I.
2. Click on System and then Troubleshoot.
3. Click on Other troubleshooters.
4. Find Windows Security under Most frequent and click Run next to it.

Follow the on-screen instructions and allow the troubleshooter to attempt to fix any detected issues.

9. Reset Windows Security App

If all other steps fail, resetting the Windows Security app to its default settings can sometimes resolve persistent issues.

Resetting Windows Security App:

1. Open Settings (Windows Key + I).
2. Click on Apps and then Installed apps.
3. Search for Windows Security.
4. Click the three dots menu next to Windows Security and select Advanced options.
5. Scroll down to the Reset section and click Reset.
6. Confirm the reset when prompted.

Alt text: Windows Settings showing Advanced options for Windows Security App with the Reset button highlighted.

After resetting, restart your computer and check if Windows Defender scan is now functioning.

Conclusion

Addressing a non-working Windows Defender Antivirus scan is critical for maintaining the security of your system. By systematically following these troubleshooting steps, from checking service statuses to resetting the application, you can effectively diagnose and resolve most issues that prevent Windows Defender from scanning properly. Regularly ensure your antivirus is functioning to protect against evolving cyber threats and maintain a secure computing environment.