On EX4100 and EX4100-VC switches, alarms related to fan underspeed or overspeed may be observed on the FPCs when fan speed falls below or exceeds predefined thresholds.

These alarms can appear even when the fans are functioning normally. This issue has been addressed in newer JUNOS software releases.

There is no service impact associated with these alarms.

Customers may observe the following alarms and log messages on the switch

root@switch> show chassis alarms no-forwarding

1 alarms currently active
Alarm time               Class  Description
 <date>                  Minor  FPC X Fan X Spinning Underspeed

Fan Underspeed messages:

 <date> switch craftd[21980]: Minor alarm set, FPC X Fan X Spinning Underspeed
<date> switch alarmd[21739]: Alarm set: FAN id=XXX, color=YELLOW, class=CHASSIS, reason=FPC X Fan X Spinning Underspeed

Or 

root@switch> show chassis alarms no-forwarding

1 alarms currently active
Alarm time               Class  Description
 <date>                  Minor  FPC X Fan X Spinning Overspeed

Fan overspeed messages: 

<date> switch craftd[18098]: Minor alarm set, FPC X Fan X Spinning Overspeed
<date> switch alarmd[17879]: Alarm cleared: FAN id=XXX, color=YELLOW, class=CHASSIS, reason=FPC X Fan X Spinning Overspeed

This issue has been fixed under PR 1875603(https://prsearch.juniper.net/problemreport/PR1875603) 

The Fix will be available in the following Junos releases:

• junos:22.4R3-S8
• junos:23.4R2-S5
• junos:24.2R2-S1
• junos:24.2R2-S2
• junos:24.4R2
• junos:25.2R1
• junos:25.3R1
• junos:25.4R1

Additionally, the PR will have an enhancement to remove & ignore the fan speed alarms with the command: 
set chassis alarm ignore-fan-speed-check

2024-04-18 : Article Created

2025-02-20: Updated PR to PR1848292, previous PR was removed from public view as versions had the issue still present