Fan issues with R520 Server

My Client is having some intermittent issues with the fans on his R520 server. I have included some of the reports from the unit , initial issues and reports after the re-boot.

Our question is do you think it may be a faulty fan sensor(s) or the fans themselves? Any input would be greatly appreciated !

[View:/cfs-file/__key/communityserver-discussions-components-files/956/5557.Avigilon-Dell-Server-issues.docx:550:0][View:/cfs-file/__key/communityserver-discussions-components-files/956/6560.Avigilon-Fan-Failure_2D00_Server-rebooted.docx:550:0]