KB 655076 - How to Diagnose Fan Module Failure on Cisco Catalyst & NX-OS Switches?
1.Overview
This document provides a systematic guide to diagnosing fan
module failures on Cisco Catalyst switches running IOS/XE and Cisco Nexus
switches running NX-OS. Fan failures can lead to overheating and switch
shutdown if not addressed promptly. This guide helps differentiate between
genuine hardware failures, software false positives, and environmental issues.
2.Scope
- Hardware Platforms:
- Cisco Catalyst Series: Specifically those running IOS and IOS-XE (e.g., Catalyst 9200, 9300, 9400, 9500, 3850, 3650).
- Cisco Nexus Series: Specifically those running NX-OS (e.g., Nexus 9000, 7000, 3000, MDS Storage Switches).
2.1 Initial Verification: Check Physical and LED Indicators
Before diving into complex commands, a physical
inspection is crucial.
- Visual Inspection: Open the switch chassis and visually confirm if the fan module is spinning. A fan that appears stationary while others are spinning indicates a potential failure .
- LED Status: Check the Status (STS) LED on the fan module itself.
- Green: The module is operating normally .
- Amber/Red (or not lit): Indicates a failure or that the module is not properly seated .
- Airflow Direction Mismatch: On Nexus switches, ensure all fan and power supply modules have the same airflow direction (e.g., all port-side exhaust with blue stripes, or all port-side intake with purple stripes). Mixing airflow directions can cause overheating and errors .
3. Diagnostic Commands (CLI)
Access the switch CLI to gather detailed status information.
For NX-OS (Nexus & MDS)
Use the show environment command family.
switch# show environment fan
Look for the Status field. Values include Ok, Failure, Absent,
or Shutdown .
For detailed LED status on newer NX-OS versions (9.3(2) and later):
switch# show environment fan detail
This command shows the LED color (Green/Amber) for each fan
module .
On some platforms like the MDS 9513, a failure status may also list
the specific individual fan numbers that have failed within the module.
For Catalyst (IOS/XE)
Use the following commands:
switch# show env fan
switch# show environment status
switch# show logging | include FAN
Check the RPM (Revolutions Per Minute) values for each fan.
An RPM value of "0" or a value significantly lower than the other
fans often indicates a stall or failure .
4. Analyzing Syslog Messages
The switch logs specific messages related to hardware
health.
Common Fan Error Messages
4.1. Replacement and Handling Guidelines
If you confirm a genuine hardware failure, follow these
guidelines during replacement
Hot-Swap Procedures
- Nexus Switches: You must replace a failed fan module within 2 minutes to prevent the switch from overheating and shutting down.
- MDS Switches: You must replace the module within 5 minutes .
Compatibility Checks
- Airflow Matching: When replacing a fan, ensure the new module's airflow direction (usually indicated by a colored stripe on the handle) matches the other modules in the chassis. Mismatched airflow voids the cooling design .
- Part Numbers: Ensure the replacement fan tray is designed for your specific chassis.
Post-Replacement Verification
- After inserting the new module, verify that the STS LED turns green .
- Re-run the show environment fan command to confirm the status is now Ok.
5.References
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