Windows Defender cannot complete a scan on my Windows 11 PC. Just before the scan finishes, it reports that the threat service has stopped. If I try to restart it, Windows says the last scan is unavailable even though I just attempted one. The last successful scan was on August 14.
I have already tried running SFC and DISM, removing and updating Defender definitions with MpCmdRun.exe, toggling Tamper Protection through the Registry, installing Windows updates, and repeating the troubleshooting steps in Safe Mode. None of these fixed the problem. Are there any other solutions I should try?
PC specifications: Ryzen 5 5600, Asus Prime 5070 12GB OC, MSI B550M Pro-VDH WiFi, 16GB DDR4-3600 RAM, TeamGroup MP33 1TB SSD, Corsair CX750 PSU, Windows 11.
3 Answers
If Defender is maxing out the CPU during scans, you can limit its scan load in an elevated PowerShell window with `Set-MpPreference -ScanAvgCPULoadFactor 15`. This will make scans less demanding, but it probably will not fix the service-crash error itself.
As a temporary check, you can install a reputable on-demand antivirus scanner and run a second-opinion scan. That can help distinguish a broken Defender installation from an actual malware problem. Avoid running two real-time antivirus programs at the same time; use the additional tool only for scanning or disable its real-time protection.
Several people appear to be seeing the same Defender failure after a recent Windows update, so this may be a bug rather than a problem unique to your installation. If a custom scan still works, that also points toward an issue with the quick-scan process. Check for another Defender or Windows update and monitor for a fix.
Custom scans work for me too, while quick scans crash every time. Everything was fine until the latest update, so the update theory seems likely.