After an upgrade, customer started noticing 'Outer Fan running at over speed' alarms for multiple fan trays, in multiple routers

Aug 22 00:02:23 JTAC alarmd[90893]: %DAEMON-4: Alarm set: FAN id=253755536, color=YELLOW, class=CHASSIS, reason=Fan Tray 2 Pair 0 Outer Fan running at over speed

Aug 22 00:02:30 JTAC alarmd[90893]: %DAEMON-4: Alarm cleared: FAN id=253755536, color=YELLOW, class=CHASSIS, reason=Fan Tray 2 Pair 0 Outer Fan running at over speed

Aug 22 00:11:13 JTAC alarmd[90893]: %DAEMON-4: Alarm set: FAN id=252706960, color=YELLOW, class=CHASSIS, reason=Fan Tray 1 Pair 0 Outer Fan running at over speed

Aug 22 00:11:26 JTAC alarmd[90893]: %DAEMON-4: Alarm cleared: FAN id=252706960, color=YELLOW, class=CHASSIS, reason=Fan Tray 1 Pair 0 Outer Fan running at over speed

labroot@JTAC> show chassis fan 

   Item           Status  % RPM   Measurement

   Fan Tray 0 Fan 0     OK    30%    7168 RPM         

   Fan Tray 0 Fan 1     OK    30%    6784 RPM         

   Fan Tray 1 Fan 0     OK    30%    7296 RPM         

   Fan Tray 1 Fan 1     OK    30%    6784 RPM         

   Fan Tray 2 Fan 0     OK    30%    7296 RPM         

   Fan Tray 2 Fan 1     OK    30%    6784 RPM   

This is fixed via below PR.

https://prsearch.juniper.net/problemreport/PR1818517

For MX10003 fan min and max threshold were -40 and +20 set. If fan RPM goes below/beyond those RPM, s/w start raising alarms.

Similarly for MX204 fan min and max threshold were -20 and +20 set.

After discussing with h/w team, min & max threshold values are now decided -40 and +40. Due to this FAN RPM will be in bandwidth and no alarm will be seen.

The PR fix will have the threshold modified.

There is no workaround for the issue & going with fixed release is the available option.