Azure AD Connect no longer synchronizes and displays the error AzureADConnect has stopped working

Problem

You’ve noticed that the Azure AD Connect server in the on-premise environment is no longer synchronizing with Azure AD and attempting to launch the synchronization engine displays the following error:

AzureADConnect has stopped working

Problem Event Name: CLR20r3

Problem Signature01: AzureADConnect.exe

Attempting to run an AD Sync via PowerShell will indicate that the Synchronization service isn’t running:

Windows PowerShell

Copyright (C) 2014 Microsoft Corporation. All rights reserved.

PS C:\Windows\system32> Start-ADSyncSyncCycle -PolicyType Delta

Start-ADSyncSyncCycle : Synchronization Service is not running.

At line:1 char:1

+ Start-ADSyncSyncCycle -PolicyType Delta

+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

+ CategoryInfo : WriteError: (Microsoft.Ident...ADSyncSyncCycle:StartADSyncSyncCycle) [Start-ADSyncSyncCy

cle], InvalidOperationException

+ FullyQualifiedErrorId : Synchronization Service is not running.,Microsoft.IdentityManagement.PowerShell.Cmdlet.S

tartADSyncSyncCycle

PS C:\Windows\system32>

Solution

One of the reasons why the above errors would be thrown is if the AD Connect server has run out of drive space on the C drive. Increasing the C drive space or cleaning up unneeded files to create space will correct the issue: