Common Drive Fault Codes & Troubleshooting Methods

Variable Frequency Drives (VFDs) and servo drives include protection mechanisms to prevent damage to motors, power electronics, and connected systems. When a fault is detected, the drive generates a fault code indicating the nature of the problem. A systematic understanding of these codes is essential for accurate diagnostics and rapid fault resolution.

For drive selection and related product families, you can review our frequency converters category and broader motor control solutions.

1) Overcurrent Fault (OC)

Technical Description: Overcurrent is triggered when output current exceeds the drive protection threshold, typically monitored via inverter-stage current sensors.

Possible Root Causes:

• Mechanical overload or locked rotor
• Phase-to-phase or phase-to-ground short circuit
• Incorrect motor parameters (rated current, power, voltage)
• Excessively short acceleration time

Technical Troubleshooting Steps:

• Measure motor phase resistance and insulation
• Verify motor nameplate data and parameter settings
• Increase acceleration ramp time
• Inspect power cables and motor terminals

If your issue is related to the motor side, also review our industrial motors section for common motor categories used with drives.

2) Overvoltage Fault (OV)

Technical Description: Overvoltage occurs when DC bus voltage exceeds the allowable limit, often due to regenerative energy during deceleration.

Possible Root Causes:

• Rapid deceleration without energy dissipation
• High inertia loads
• Unstable or fluctuating supply voltage

Technical Troubleshooting Steps:

• Extend deceleration time
• Install/verify braking resistor and chopper operation
• Measure DC bus voltage under dynamic conditions

3) Undervoltage Fault (UV)

Technical Description: Undervoltage is generated when input or DC bus voltage drops below the minimum operational threshold needed for stable inverter operation.

Possible Root Causes:

• Supply voltage dips or phase loss
• Loose or degraded power connections
• Inadequate power supply capacity

Technical Troubleshooting Steps:

• Monitor input voltage across all phases
• Check upstream contactors, breakers, and transformers
• Verify correct power supply sizing

4) Overtemperature Fault (OH / OT)

Technical Description: This fault indicates internal drive or power module temperature has exceeded limits, detected by thermal sensors.

Possible Root Causes:

• Insufficient cooling or airflow
• High ambient temperature
• Continuous operation at high load

Technical Troubleshooting Steps:

• Clean/replace cooling fans and air filters
• Improve cabinet ventilation
• Measure ambient and internal temperatures
• Reduce load or switching frequency if necessary

5) Communication Fault (COM / BUS)

Technical Description: Communication faults occur when data exchange between drive and PLC/DCS/HMI is interrupted or corrupted.

Possible Root Causes:

• Faulty communication cables or connectors
• Incorrect protocol or baud rate settings
• Network termination or grounding issues

Technical Troubleshooting Steps:

• Verify cable shielding and grounding
• Check communication parameters and node addresses
• Use diagnostic tools or network analyzers

Conclusion

Drive fault codes provide valuable diagnostic insight into electrical, mechanical, and thermal issues within industrial motion systems. A methodical troubleshooting approach—based on measurements, parameter verification, and system-level analysis—enables faster fault recovery and improved reliability. For brand-based drive ecosystems, you can also review ABB drive systems and compatible components.