Microsoft Defender will not complete a full scan - Threat service has stopped

I am experiencing an issue with Microsoft Defender on my Windows 11 system. I cannot run Quick Scan, Full Scan, or Microsoft Defender Offline Scan successfully.

What happens:

• When I start any scan (Quick, Full, or Offline), it begins normally.

However, after approximately 2–3 minutes, the scan stops abruptly without any error message.

The program then returns to the "Virus & threat protection" screen and shows: "No current threats. Last scan: unavailable".

Sometimes it also prompts: "Restart the protection service" or displays a message that the service needs to be restarted.

When I run the Offline scan, the process hangs and freezes at 91% and never completes.

I can still scan individual files manually, and those scans complete successfully. Only full system scans fail.

What I have already tried (with no success):

Ran sfc /scannow – it completed but did not fix the issue.

Ran DISM /Online /Cleanup-Image /RestoreHealth – it repaired some files, but Defender still fails.

Performed an in-place upgrade (repair installation) using the Windows installation media (as recommended by Microsoft Support) – the issue persists.

Installed all Windows updates (including optional ones).

Reset the Windows Security app via Settings.

Checked the registry for policies like DisableAntiSpyware – no such entries found.

Run third-party scanners (Dr.Web, Kaspersky) – they found no active malware.

System information:

Edition: Windows 11 Pro

Version: 24H2

Installation date: 10 June 2025

OS build: 26100.9168

Windows Feature Experience Pack: 1000.26100.344.0

Defender platform version (from event log): 4.18.26070.9

Additional details:

The Event Viewer shows the following error (Event ID 1000) when the scan fails:

Faulting application: MsMpEng.exe

  Faulting module: mpengine.dll
  
     Exception code: 0xc0000005 (Access Violation)
     

It seems that the mpengine.dll file is corrupted and cannot be replaced by normal updates. I would like to know if there is a tool or method to completely reinstall the Microsoft Defender engine and its components without reinstalling the whole operating system.

Please advise on the next steps. I can provide additional logs or diagnostic data upon request.

Thank you for your assistance.I am experiencing an issue with Microsoft Defender on my Windows 11 system. I cannot run Quick Scan, Full Scan, or Microsoft Defender Offline Scan successfully.

What happens:

When I start any scan (Quick, Full, or Offline), it begins normally.

However, after approximately 2–3 minutes, the scan stops abruptly without any error message.

The program then returns to the "Virus & threat protection" screen and shows: "No current threats. Last scan: unavailable".

Sometimes it also prompts: "Restart the protection service" or displays a message that the service needs to be restarted.

When I run the Offline scan, the process hangs and freezes at 91% and never completes.

I can still scan individual files manually, and those scans complete successfully. Only full system scans fail.

What I have already tried (with no success):

Ran sfc /scannow – it completed but did not fix the issue.

Ran DISM /Online /Cleanup-Image /RestoreHealth – it repaired some files, but Defender still fails.

Performed an in-place upgrade (repair installation) using the Windows installation media (as recommended by Microsoft Support) – the issue persists.

Installed all Windows updates (including optional ones).

Reset the Windows Security app via Settings.

Checked the registry for policies like DisableAntiSpyware – no such entries found.

Run third-party scanners (Dr.Web, Kaspersky) – they found no active malware.

System information:

Edition: Windows 11 Pro

Version: 24H2

Installation date: 10 June 2025

OS build: 26100.9168

Windows Feature Experience Pack: 1000.26100.344.0

Defender platform version (from event log): 4.18.26070.9

Additional details:

The Event Viewer shows the following error (Event ID 1000) when the scan fails:

Faulting application: MsMpEng.exe

  Faulting module: mpengine.dll
  
     Exception code: 0xc0000005 (Access Violation)
     

It seems that the mpengine.dll file is corrupted and cannot be replaced by normal updates. I would like to know if there is a tool or method to completely reinstall the Microsoft Defender engine and its components without reinstalling the whole operating system.

Please advise on the next steps. I can provide additional logs or diagnostic data upon request.

Thank you for your assistance.