VFD Troubleshooting Guide

Is your VFD showing unusual behavior or unexpected faults?
Don’t worry—variable frequency drives (VFDs) may occasionally experience operational anomalies, but most issues can be traced and resolved with proper diagnostics.
This guide will help you become a VFD fault decoding expert,we’ll walk you through the common symptoms, explain what they mean, and provide step-by-step solutions using proven industrial techniques.

VFD troubleshooting diagram showing overcurrent issues

What Is a VFD Fault?

In simple terms, a VFD fault is when your variable frequency drive detects that its own operation, the motor, or the load has deviated from the safe “green zone,” triggering a protective shutdown or alarm. This is like pressing the emergency pause button on the entire variable frequency drive control system.

Types of VFD Faults

Soft Faults
These are ypically caused by transient conditions such as:
  • Momentary overcurrent
  • Minor overheating
  • Temporary voltage fluctuations (e.g., power grid instability)
These faults are usually non-critical and can often be cleared automatically or via the reset function on the VFD keypad.
Hard Faults
These indicate severe or persistent issues involving:
  • Internal component failure (e.g., IGBT short circuits)
  • Direct ground faults
  • Severe overload or locked-rotor conditions
Hard faults cannot be automatically reset. They require inspection by qualified technicians to diagnose and correct the root cause—whether inside the VFD or within the connected motor/load—before safe restart is possible.
Modern VFDs use built-in digital displays or LED indicators to report fault status via standardized error codes.Examples:(Err 05: Deceleration Overcurrent/Overvoltage Fault,Err 10: Inverter Overload Fault)Interpreting these fault codes is akin to reading the “language” of the drive—serving as the critical first step in accurate, timely fault diagnosis and recovery.

Common Causes of VFD Troubleshooting Issues

Cause Type

Description

Linked Faults

Harsh Environment

Heat, moisture, dust, vibration

vfd overcurrent fault, ground fault

Electrical Failures

Loose wires, phase loss, voltage dips

vfd fault, overcurrent fault on vfd

Load/Motor Mismatch

Wrong settings, oversized loads

vfd drive repair, frequency drive motor

Internal Component Failures

Aging capacitors, IGBTs

electrical vfd, vfd mechanical

Types of VFD Faults and Their Symptoms

When your variable frequency drive (VFD) shuts down or flashes a warning light, it’s not just malfunctioning—it’s issuing a health report.
Each VFD fault code and symptom corresponds to a specific issue, and understanding these signals is key to fast and accurate troubleshooting. Here’s how to interpret the “vital signs” of your VFD:

Fault Type

Typical Symptoms

Common Causes

Recommended Action

Catastrophic Failure

Burning smell- Sparks- Blown fuses

IGBT or capacitor failure- Severe overvoltage- Cooling system failure

Disconnect power immediately; inspect power board and internal components; replace damaged parts.

Power Interruption

Instant shutdown- UV (Undervoltage)- Phase Loss alarm

Grid sag or brownout- Power outage or upstream breaker trip

Check incoming power supply, verify voltage stability, and restart after source is confirmed stable.

Intermittent Fault

Random errors (OV, OH, etc.)- Motor vibration or jerking- Unstable ops

Loose terminals- EMI/noise- Aging capacitors- Blocked cooling path- Tight parameter margins

Inspect wiring, signal shielding, cooling system; adjust acceleration/deceleration parameters.

Overcurrent / Overload

OC / OL codes lit- Sudden motor stop- Acceleration surge or smoke

Impeller jam- Motor short circuit- VFD undersized- Output cable short or overload

Check motor load and shaft, measure winding resistance, verify drive sizing and output cable condition.

Ground Fault (GF)

GF alarm- Tingling cabinet- Frequent RCD trips

Motor/cable insulation failure- Moisture ingress- Corrosion-induced short circuit

Use megohmmeter to test motor, cable, and VFD insulation; isolate power immediately for safety.

Think of VFD fault codes not as random glitches—but as the drive’s way of speaking. The better you understand its “language,” the faster you can restore system health and avoid costly downtime.

VFD Troubleshooting Step-by-Step Checklist

1.Visual Inspection

Immediately disconnect the power supply and perform a careful visual check for signs of physical damage—such as burn marks, bulging capacitors, loose terminal connections, non-functioning cooling fans, or dust accumulation. This is the first and most essential step in effectively troubleshooting VFD drives.

2.Verify Power Supply and Wiring

Use a multimeter to confirm:
  • Input voltage and phase configuration are correct
  • Input/output terminals are tightly secured and free of corrosion
  • DC bus voltage remains stable and within the rated range
A clean, stable power supply is a prerequisite for reliable VFD operation and reduces the need for premature vfd drive repair.

3.Check Control Signals

Verify that start/stop signals are properly transmitted (check terminal block voltage or external contact signals).
Measure the speed reference input (analog or communication) to ensure it’s stable, with no noise, interference, or signal loss.
Control circuit issues are among the most frequent root causes when troubleshooting VFD drives.

4.Interpret Fault Codes

This is a critical diagnostic step. Regularly review the VFD user manual and understand common fault codes (e.g., OC – overcurrent, UV – undervoltage, OH – overheating).
These codes offer direct insight into the drive’s operating condition and are key references in any effective vfd drive repair process.

5.Check the Motor and Wiring

After powering off:
  • Confirm proper torque on output terminals
  • Use a megohmmeter to test insulation integrity of motor and cables
  • Ensure motor model, power rating, and electrical parameters are fully compatible with VFD settings
Mismatched motor parameters can cause VFD overheating and failure, making this step crucial for both repair and vfd maintenance planning.

6.Assess Environmental Factors

Check internal cabinet temperature (ideally below 40°C), ventilation, humidity levels, presence of dust, and corrosive gases.
Harsh environmental conditions can significantly reduce equipment lifespan, making environmental control a key part of preventive vfd maintenance.

7.Document the Entire Process

Keep detailed records of all inspection results, measurements, parameter changes, and final system status.
Thorough documentation supports future repairs, ongoing vfd maintenance, and root cause analysis for persistent or recurring issues.

Using Tools to Diagnose VFD Problems

Tool

Application

Multimeter

Checking input/output voltage, resistance

Oscilloscope

Capturing transient faults or control signals

VFD Software

Real-time monitoring and diagnostic

VFD Fault Code Reference Table

Fault Code

Description

Likely Cause

Recommended Fix

OC

Overcurrent

Load spike, short

Check load & motor

GF

Ground fault

Insulation failure

Check motor wiring

OH

Overheating

Poor cooling

Clean fans/heatsink

UV

Undervoltage

Phase loss, dip

Check input voltage

How to Prevent Future VFD Failures

To prevent unexpected shutdowns of VFD drives, it is essential to implement an active VFD maintenance plan:

Strictly adhere to a regular maintenance schedule: Establish and enforce a maintenance schedule based on operating hours. Key areas include: Regularly clean air filters and cooling fans (recommended monthly/quarterly) to ensure proper heat dissipation; inspect and tighten all electrical connections (using a torque wrench); monitor DC bus voltage ripple (indicating capacitor health).

​ Critical data and spare parts management:​​ ​ Back up all VFD parameters (including motor data and application parameters) to ensure rapid recovery after a fault. Keep critical VFD components in stock, such as cooling fans and spare control cards (if applicable), to minimize downtime.

Empower maintenance teams: Conduct VFD troubleshooting training. Ensure maintenance personnel not only know how to operate the equipment but also understand the principles, identify early warning signs (such as abnormal noise or slight temperature rise), and master standardized VFD maintenance routines, such as safe cleaning, parameter backup, and basic measurements.

Core: Transform reactive repairs into proactive maintenance by standardizing operations, controlling the environment, and enhancing personnel skills to maximize VFD reliability and service life.

Conclusion

Efficient and safe VFD troubleshooting depends on a systematic approach: Always follow power-off safety procedures. Start with a visual inspection and gradually verify the power supply, signals, wiring, and environment. Accurate interpretation of fault codes is a core skill; be sure to consult the manual. After a thorough investigation, be sure to back up all parameters and record the process. Mastering this process, combined with preventive VFD maintenance, can significantly reduce downtime and ensure production.