Event ID 666Failed due to SQL deadlock

What to check

Usually transient; if it repeats, check SQL health on the Connect server.

Find it with PowerShell

Run on the machine that logs it.

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2Get-WinEvent -FilterHashtable @{ LogName = 'Application'; Id = 666 } -MaxEvents 50 |
    Format-List TimeCreated, Id, Message

Hunt for it in Sentinel or Log Analytics

This works once a data collection rule sends the Application log to your workspace, where it lands in the Event table.

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5Event
| where TimeGenerated > ago(7d)
| where EventLog == "Application" and EventID == 666
| project TimeGenerated, Computer, Source, RenderedDescription
| order by TimeGenerated desc

Related Entra Connect events

• Event ID 601: Password hash sync manager starting
• Event ID 607: Password hash sync could not start
• Event ID 609: Password hash sync stopped
• Event ID 611: Error during password hash sync for a domain
• Event ID 613: Paused: full sync not completed
• Event ID 616: Connection to preferred DC failed
• Event ID 617: Full password hash sync started for forest
• Event ID 621: Full password hash sync attempt failed

Search all 123 event IDs →