VFD (Variable Frequency Drive) Fault Codes

What is a VFD (Variable Frequency Drive)?

A Variable Frequency Drive (VFD) controls AC induction motor speed and torque by adjusting frequency and voltage. 

VFDs increase energy efficiency, smooth acceleration and deceleration and accurate process control that is making them popular in industrial, commercial and HVAC applications.

A VFD monitors voltage, current, temperature & communication signals to protect itself, the motor and the driven equipment like any advanced power electronics device. 

The drive trips as well as displays a fault code on its keypad (or) operator panel when a monitored parameter exceeds its safe operating range.

Technicians, maintenance engineers & plant operators require these trouble codes to diagnose issues quickly, reduce downtime & avoid equipment damage.

This post details the twenty most frequent VFD fault codes, their causes and troubleshooting guidance in an easy-to-reference structure. 

It is a basic technical reference; failure code nomenclature and severity limits differ between manufacturers (such as ABB, Siemens, Danfoss, Schneider Electric, Delta and Yaskawa), so check the drive’s manufacturer manual for site-specific data.

Why Fault Codes Important?

Fault codes serve as the drive’s self-diagnostic language. 

A VFD reports a specific alphanumeric code that reduces the problem to a particular subsystem which is power supply, motor circuit, cooling system, control electronics (or) external interlocks. 

This dramatically reduces troubleshooting time compared to inspecting the entire system.

• Faster fault isolation & reduced mean-time-to-repair (MTTR).
• Protection of the electric drives power electronics (IGBTs, capacitors, rectifiers) from cascading damage.
• Protection of the connected motor from thermal (or) electrical overstress.
• Improved safety for personnel by tripping before the hazardous conditions develop.
• Data for predictive & preventive maintenance planning.

Complete 20 Fault Code Reference Table

The table below lists 20 commonly encountered VFD fault codes along with their standard meanings. 

Codes are grouped loosely by category i.e., electrical (voltage/current), thermal, mechanical and control/communication faults.

S. No	Fault Code	Fault Name	Description / Meaning
1	OV	Over Voltage	DC bus voltage rises above the drive’s allowable upper limit.
2	UV	Under Voltage	DC bus voltage falls below the drive’s allowable lower limit.
3	OC	Over Current	Output current exceeds the allowable limit of the drive.
4	OL	Over Load	The drive or connected motor is overloaded beyond rated capacity.
5	OH	Over Heat	Heatsink temperature exceeds the safe operating limit.
6	OL1	Motor Overload	Motor current exceeds its rated value for a prolonged period.
7	GF	Ground Fault	Current leakage to ground has been detected.
8	PHL	Phase Loss	One or more input or output phases are missing.
9	SC	Output Short Circuit	A short circuit exists in the motor or output wiring.
10	CE	Communication Error	Communication failure between the drive and an external device.
11	ENC	Encoder Error	Encoder feedback signal is lost or abnormal.
12	EEP	EEPROM Error	Memory read (or) write error within the drive.
13	CPU	CPU Error	Internal processor (CPU) fault detected.
14	FAN	Fan Fault	Cooling fan is not working (or) has become disconnected.
15	BRF	Brake Resistor Fault	Brake resistor is not connected and open-circuited (or) overheated.
16	EXT	External Trip	A fault signal was received from an external terminal (or) safety circuit.
17	StP	Stall Prevention	Motor stall detected due to high load (or) mechanical jam.
18	IPF	Input Phase Failure	One (or) more input phases to the drive are missing.
19	OPF	Output Phase Failure	One (or) more output phases to the motor are missing.
20	E-STOP	Emergency Stop	Drive has been stopped by an emergency stop signal.

Key Fault Categories

Voltage-Related Faults (OV, UV)

Fault

• Over Voltage (OV) and 
• Under Voltage (UV) faults 

relate to the DC bus, the intermediate stage inside the VFD where incoming AC power is rectified to DC before being inverted back to variable-frequency AC for the motor. 

Over-voltage often occurs during rapid deceleration when the motor regenerates energy back into the DC bus faster than it can be dissipated (or) due to high incoming line voltage. 

Under-voltage is typically caused by a weak or sagging power supply, loose input wiring (or) a partial loss of input phase. 

Solution

Solutions include adding braking resistors, extending deceleration ramp times, and verifying supply voltage stability.

Current-Related Faults (OC, OL, OL1, SC)

Fault

Over Current (OC) and short-circuit (SC) faults indicate excessive current flow often caused by a 

• Motor winding fault, 
• Cable insulation breakdown, 
• Mechanical jam (or) an aggressive acceleration ramp. 

Overload faults (OL, OL1) are triggered when current remains above the rated value for an extended time which is signaling that the motor (or) driven load is working harder than designed. 

Solution

Checking motor alignment, load conditions, and cable integrity typically resolves these issues.

Thermal Faults (OH, FAN)

Fault

Over Heat (OH) faults occur when the heatsink temperature, monitored by an internal sensor, exceeds safe limits that is usually due to blocked ventilation, high ambient temperature (or) a failed cooling fan. 

The Fan Fault (FAN) code specifically flags a non-operational (or) disconnected cooling fan which should be addressed immediately since continued operation without cooling risks permanent damage to power semiconductors.

Phase and Ground Faults (GF, PHL, IPF, OPF)

Fault

Ground Fault (GF) indicates current leakage from a phase conductor to earth ground, often due to insulation degradation in motor windings (or) cabling. 

Phase-related faults (PHL, IPF, OPF) indicate a missing input or output phase commonly caused by a blown fuse, a loose terminal connection (or) a failed contactor. 

Solution

These faults protect the drive from unbalanced operation, which can cause severe overheating.

Control, Communication and Mechanical Faults (CE, ENC, EEP, CPU, BRF, EXT, StP, E-STOP)

Fault

This group covers faults outside the main power circuit. 

Communication Error (CE) points to a broken link between the drive and a PLC, HMI (or) fieldbus network. 

Encoder Error (ENC) relates to feedback loss in closed-loop vector control applications. 

EEPROM (EEP) and CPU errors indicate internal memory or processor faults, usually requiring a drive reset (or) in persistent cases as a replacement. 

Brake Resistor Fault (BRF) flags a disconnected (or) overheated dynamic braking resistor. 

External Trip (EXT) reflects a signal from an external safety device such as a door interlock or thermal switch. 

Stall Prevention (StP) detects a stalled motor condition from an excessive load (or) jamming & Emergency Stop (E-STOP) that confirms the drive halted because the physical emergency stop circuit was activated.

General Troubleshooting Method

• Record the exact fault code, time of occurrence & operating conditions before resetting the drive.
• Consult the manufacturer manual for the accurate details since codes can differ slightly between brands & firmware versions.
• Inspect all the relevant subsystem initially which is power supply for voltage faults, motor & cabling for current faults, cooling system for thermal faults.
• Check for the loose connections, damaged insulation & correct parameter settings (acceleration/deceleration ramps & current limits).
• Only reset & restart the electrical drive once the root cause has been identified & corrected to avoid repeated nuisance tripping (or) electrical equipment damage.
• Maintain a fault log over time to identify (findings) the recurring issues that may indicate (show) a developing mechanical (or) electrical problem.

Important Note

Fault codes may vary across different VFD brands and firmware versions.

Always refer to the manufacturer manual for the exact details specific to your drive model.

Conclusion

VFD fault codes are the most important diagnostic tools that simplify internal drive conditions into proper actionable alerts. 

This post explained about 20 fault codes for voltage, current, thermal, phase, ground & control related faults. 

Understanding them helps maintenance personnel respond quickly & accurately minimizing unplanned downtime & extending drive and motor life. 

To ensure accuracy always utilize this reference with the drives official documentation because implementation details differ by manufacturer.