Fix Azure AD Connect Sync Service Not Running – Windows Server 2016/2019/2022 2026

This is the quickest method to resolve the immediate issue and restore synchronization.

1. Press Windows + R to open the Run dialog
2. Type services.msc and press Enter
3. In the Services console, scroll down and locate Microsoft Azure AD Sync
4. Check the service status - it should show as Stopped
5. Right-click on Microsoft Azure AD Sync and select Properties
6. Verify the Startup type is set to Automatic. If not, change it to Automatic
7. Click Apply, then click Start to start the service
8. Wait for the service status to change to Running
9. Click OK to close the Properties dialog

Configure automatic recovery to prevent future service failures from causing extended downtime.

1. Open Services console (services.msc)
2. Right-click Microsoft Azure AD Sync and select Properties
3. Click the Recovery tab
4. Set the following recovery options:
   • First failure: Restart the Service
   • Second failure: Restart the Service
   • Subsequent failures: Restart the Service
5. Set Reset fail count after: 1 days
6. Set Restart service after: 2 minutes
7. Click Apply and OK
8. Restart the service to test the configuration

Fix service dependencies and permissions that may prevent the ADSync service from starting properly.

1. Open an elevated Command Prompt as Administrator
2. Stop the Azure AD Sync service:
   

   net stop ADSync

3. Reset service dependencies:
   

   sc config ADSync depend= RpcSs/EventLog

4. Verify the service account permissions:
   

   Get-WmiObject -Class Win32_Service -Filter "Name='ADSync'" | Select-Object Name, StartName

5. Grant the service account "Log on as a service" right:
   • Open Local Security Policy (secpol.msc)
   • Navigate to Local Policies → User Rights Assignment
   • Double-click Log on as a service
   • Add the ADSync service account if not present
6. Start the service:
   

   net start ADSync

7. Check service status:
   

   Get-Service ADSync

Use the Azure AD Connect repair function to fix corrupted service configurations and restore proper functionality.

1. Download the latest Azure AD Connect installer from the Microsoft Download Center
2. Run the installer as Administrator
3. On the welcome screen, select Repair or reinstall an existing Azure AD Connect installation
4. Click Next and accept the license terms
5. On the repair options screen, select Repair
6. The installer will:
   • Repair service configurations
   • Reset registry entries
   • Restore default permissions
   • Update service dependencies
7. Wait for the repair process to complete
8. Click Finish when the repair is successful
9. Restart the server to ensure all changes take effect

Perform advanced diagnostics to identify and resolve underlying issues preventing service startup.

1. Check Windows Event Logs for service startup errors:
   

   Get-EventLog -LogName System -Source "Service Control Manager" -After (Get-Date).AddDays(-1) | Where-Object {$_.Message -like "*ADSync*"}

2. Examine Azure AD Connect specific logs:
   

   Get-ChildItem "C:\ProgramData\AADConnect\trace-*.log" | Sort-Object LastWriteTime -Descending | Select-Object -First 5

3. Verify registry entries for the ADSync service:
   

   Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\ADSync"

4. Check database connectivity:
   

   Test-NetConnection -ComputerName localhost -Port 1433

5. If registry corruption is detected, restore from backup or recreate service entry:
   

   sc delete ADSync
   sc create ADSync binPath= "C:\Program Files\Microsoft Azure AD Sync\Bin\miiserver.exe" start= auto

6. Restart the Windows Management Instrumentation service:
   

   net stop winmgmt /y
   net start winmgmt

7. Start the ADSync service and monitor for errors