How to Diagnose Fan Module Failure on Cisco Catalyst & NX-OS Switches?

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.

Info
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):

Info
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)

Quote
Use the following commands:

Info
switch# show env fan

Info
switch# show environment status

Info
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.

Warning
Common Fan Error Messages


4.1. Replacement and Handling Guidelines

If you confirm a genuine hardware failure, follow these guidelines during replacement

Alert
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 .

Alert
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.

Alert
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