acx710 suddenly reports "FPC 0 Fan Tray 0 Fan/Blower Absent" error and the fan-tray is absent when issuing "show chassis environment"

root@ACX710> show chassis alarms no-forwarding
1 alarms currently active
Alarm time Class Description
2024-05-13 15:20:07 CST Major FPC 0 Fan Tray 0 Fan/Blower Absent
 

root@ACX710> show chassis environment no-forwarding

Class Item Status Measurement

Power Power Supply 0 OK
Temp FPC 0 CPU Sensor OK 41 degrees C / 105 degrees F
FPC 0 Power on board Sensor OK 44 degrees C / 111 degrees F
FPC 0 Switch Sensor 2 Internal OK 60 degrees C / 140 degrees F
FPC 0 Switch Sensor 2 External OK 45 degrees C / 113 degrees F
FPC 0 FPGA Sensor 3 Internal OK 46 degrees C / 114 degrees F
FPC 0 FPGA Sensor 3 External OK 48 degrees C / 118 degrees F
FPC 0 PSU Sensor OK 39 degrees C / 102 degrees F
Fans Fan Tray 0 Fan 0 Absent
Fan Tray 0 Fan 1 Absent
Fan Tray 0 Fan 2 Absent
Fan Tray 0 Fan 3 Absent
Fan Tray 0 Fan 4 Absent
 

May 13 15:20:07 ACX710 alarmd[8086]: %DAEMON-4: Alarm set: FAN id=33554576, color=RED, class=CHASSIS, reason=FPC 0 Fan Tray 0 Fan not spinning or Absent

May 13 15:20:07 ACX710 craftd[8088]: %DAEMON-4: Receive FX craftd set alarm message: color: 1 class: 100 object: 144 slot: 0 silent: 0 short_reason=FPC 0 Fan Tray 0 F long_reason=FPC 0 Fan Tray 0 Fan not spinning or Absent id=33554576 reason=33554432

May 13 15:20:07 ACX710 craftd[8088]: %DAEMON-4: Major alarm set, FPC 0 Fan Tray 0 Fan not spinning or Absent

the issue might be caused by either FAN-tray hardware failure or the system failed to detect the fan-tray.
 
1. check LCMD and chassisD are running and CPU usage is NOT high.
2: reboot the router to check if the issue persists. 
3: create a JTAC case and JTAC engineer will help to determine if an RMA is required.

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in the following example, the lcmd and chassis look fine and CPU idle is 60%, please contact JTAC for further assistance.

root@ACX710> show system processes extensive 
last pid: 50882; load averages: 1.51, 1.05, 0.95 up 92+08:01:41  15:03:19
354 threads:  5 running, 321 sleeping, 28 waiting
CPU: 2.9% user, 0.0% nice, 16.1% system, 0.1% interrupt, 80.9% idle
Mem: 223M Active, 1398M Inact, 487M Wired, 74M Buf, 1899M Free
Swap: 3072M Total, 3072M Free
 PID USERNAME  PRI NICE  SIZE  RES STATE  C  TIME  WCPU COMMAND
14387 root     35  0  74M 4240K kqread  2 226.0H  5.96% lcmd{lcmd}     
14347 root     20  0  385M  47M select  1 540:46  0.10% chassis        

 
root@ACX710> show chassis routing-engine
Routing Engine status:
 Slot 0:
  Current state         Master
  5 sec CPU utilization:
   User           14 percent          
   Background         0 percent
   Kernel          26 percent
   Interrupt         0 percent
   Idle           60 percent              <<<<<<
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