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VFD Fault Codes & Troubleshooting Guide

A practical guide to diagnosing common Variable Frequency Drive faults, understanding alarm codes and improving industrial drive reliability.

Understanding Variable Frequency Drive Faults

Variable Frequency Drives (VFDs) are the core components of modern industrial automation systems. By controlling motor speed, torque and operation efficiency, VFDs help industrial equipment achieve safer operation, higher efficiency and lower energy consumption.

However, after long-term operation under different environmental and load conditions, a drive system may experience abnormal conditions. When a fault occurs, the VFD usually displays an alarm code to help engineers quickly identify the problem and reduce troubleshooting time.

This guide introduces common VFD fault codes, possible causes and recommended solutions to help users improve maintenance efficiency and equipment reliability.

VFD Fault Diagnosis Process

1. Identify Alarm Code

Check the displayed fault code from the VFD keypad or monitoring system.

2. Analyze Cause

Evaluate motor, load, power supply and environmental conditions.

3. Correct Problem

Adjust parameters, repair wiring or solve mechanical issues.

4. Verify Operation

Restart the system and confirm stable operation.

Common VFD Fault Codes & Solutions

01. OCF - Overcurrent Fault

Possible Causes:

  • Motor stall or mechanical blockage
  • Excessive motor load
  • Incorrect motor nameplate data settings

Recommended Solutions:

  • Check whether motor or equipment is blocked
  • Confirm VFD capacity matches motor and load
  • Verify current protection settings
  • Check motor parameters and perform autotuning if required

02. OHF - VFD Overheating Fault

Possible Causes:

  • Poor ventilation
  • High ambient temperature
  • Heavy motor load
  • Blocked cooling airflow

Recommended Solutions:

  • Clean cooling channels and air filters
  • Improve cabinet ventilation
  • Reduce environmental temperature
  • Allow VFD temperature to decrease before restarting

03. OBF - Braking Overvoltage Fault

Possible Causes:

  • Acceleration/deceleration time too short
  • High inertia load
  • DC bus voltage increase during braking

Recommended Solutions:

  • Increase deceleration time
  • Enable adaptive braking function
  • Select suitable braking resistor

04. OLF - Motor Overload Fault

Possible Causes:

  • Motor operates under excessive load for a long time
  • Motor current exceeds thermal protection limit
  • Incorrect motor protection parameters

Recommended Solutions:

  • Check whether mechanical load exceeds rated capacity
  • Verify motor thermal protection settings
  • Allow motor cooling before restarting

05. OPF - Motor Phase Loss Fault

Possible Causes:

  • Motor cable disconnected or loose
  • VFD power rating much higher than motor rating
  • Motor current too low for detection
  • Incorrect motor parameters

Recommended Solutions:

  • Check motor connection and wiring terminals
  • Verify motor voltage and current parameters
  • Perform motor autotuning when required

06. SCF - Motor Short Circuit Fault

Possible Causes:

  • Damaged motor cable insulation
  • Motor insulation failure
  • IGBT power module failure
  • Output grounding leakage

Fault Types:

  • SCF1: Motor phase-to-phase or phase-to-ground short circuit
  • SCF2: Output impedance short circuit
  • SCF3: Excessive grounding leakage current

Recommended Solutions:

  • Check cable insulation condition
  • Test motor insulation resistance
  • Install motor reactor or sine wave filter for long cables
  • Check IGBT power components

07. OSF - Input Overvoltage Fault

Possible Causes:

  • Input voltage exceeds rated range
  • Large grid voltage fluctuation

Recommended Solutions:

  • Measure incoming power voltage
  • Ensure voltage remains within VFD allowable range
  • Check power supply stability

08. SLF - Communication Fault

Possible Causes:

  • Communication cable disconnected
  • Loose communication terminals
  • Incorrect timeout parameters
  • PLC or control program abnormality

Recommended Solutions:

  • Check communication wiring
  • Verify communication parameters
  • Check PLC and control system programs

09. USF - Undervoltage Fault

Possible Causes:

  • Low grid voltage
  • Unstable power supply
  • Large temporary voltage drop

Recommended Solutions:

  • Check incoming voltage
  • Improve power supply stability
  • Adjust undervoltage protection parameters

10. PHF - Input Phase Loss Fault

Possible Causes:

  • Three-phase power supply missing one phase
  • Loose input terminals
  • Incorrect power supply mode settings

Recommended Solutions:

  • Check circuit breakers and contactors
  • Verify three-phase input voltage
  • Tighten all power connections
  • Confirm supply parameter settings

Preventive Maintenance Tips for VFD Systems

Control Temperature

Keep electrical cabinets ventilated and avoid excessive ambient temperature.

Clean Regularly

Remove dust and contaminants from cooling channels and components.

Check Power Quality

Monitor voltage fluctuation and electrical connections.

Record Fault History

Analyze alarms to prevent repeated failures.

Frequently Asked Questions About VFD Faults

Overcurrent faults are usually caused by motor overload, mechanical blockage, incorrect motor parameters or unsuitable VFD selection. Check the motor condition, load and drive settings before restarting.

Ensure proper ventilation, clean cooling systems regularly and confirm that the VFD capacity matches the application requirements.

Yes. Wolong provides technical support for VFD selection, commissioning, fault diagnosis, parameter setting and maintenance.

Need Help With Your VFD Fault?

Contact Wolong technical engineers for professional troubleshooting support and drive solutions.

Technical Support Hotline:
+86 13609288011

Email:
[email protected]

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