This article lists some of the log messages or chassis alarms that are seen along with the "fan not spinning" message on devices that are running Junos OS.

Chassis Alarms / Signatures Examples:

root@hostname> show chassis alarms no-forwarding

• The following chassis alarm may be seen:   

  • Major FPC X Fan X not spinning

Log Messages / Signatures Examples:

root@hostname> show log message / show log chassisd

• The following log messages may be seen:

  • chas[XXX]: Fan X is NOT spinning correctly

  • Alarm set: FAN xxx color=RED, class=CHASSIS, reason=FPC X Fan X not spinning

Engage the technician onsite, and check for any damages/issues with the fan tray. Check whether the air inflow and surrounding temperature are normal.

For units that are mounted in a cabinet, it is important to secure sufficient clearance around the rack, without any objects (e.g. cables) blocking both the inlet and the exhaust areas of the router, and to ensure regular inspection of the air filter and its cleanliness.

It is important to physically check whether the fan is truly not spinning or it is a false alarm. Check if the damage is on the chassis side (click pictures if possible).

Check by swapping the fan tray with a known good one to check if the issue is actually with the fan tray.

Check the status by power cycling the device (reasons for this step).

• Occasionally, you will see these messages when some other component, upon which the fans depend, fails. This can be a control board or even the chassis.

• If your device has multiple fan trays and all of them report this alarm simultaneously, then this probably indicates a failure of the control board, rather than the fans. 

If a spare fan is available, test it on the faulty slot to confirm the issue. And if replacing the malfunctioning fan with a spare resolves the issue, proceed to request an RMA for the faulty fan.

Note: We recommend that you perform this activity during a maintenance window. Also, to prevent overheating, install the replacement fan tray immediately after removing the existing fan tray.

Reference Troubleshooting commands

• user> show chassis environment 

• user> show chassis fan

• user> show chassis alarms

• user> show system alarms

• user> show log messages | match fan

• user> show log chassisd | match fan

• user> test chassis fan (only available in some platforms)

• KB22575 - [EX/QFX] Major alarm set, FPC x Fan x not spinning [juniper.net]

• KB18782 - Syslog message: CHASSISD_FAN_FAILURE [juniper.net]

• KB71518 - [PTX/SRX/QFX]Major Fan Tray [X] Fan [X] Not Spinning / Fan Tray [X] is not present [juniper.net]

2024-04-25: Minor, non-technical changes

2024-03-11: Article created