Learn how to troubleshoot Yaskawa AFD fault codes and alarms, including oC, ov, Uv1, oH, oL1, oL2, GF, SC, PF and communication faults with practical solutions.
Comprehensive Troubleshooting Guide for Common Yaskawa AFD Issues: Overcurrent, Overvoltage, Overload, and More.
Yaskawa Adjustable Frequency Drives (AFDs), also commonly called variable frequency drives (VFDs) or AC drives, are built to provide precise motor control, but faults can quickly stop production when the underlying cause is not addressed. The most effective troubleshooting approach is to treat the displayed fault code as a diagnostic clue, then verify power quality, motor condition, wiring, mechanical load, cooling, and drive parameters before resetting the drive. This guide covers the most common Yaskawa AFD fault codes and alarms—including oC, ov, Uv1, oH/oH1, oL1, oL2, GF, SC, PF, LF, EF, bUS and communication-related faults—with practical corrective actions for industrial maintenance personnel.
Important: Yaskawa fault codes can vary by drive family and firmware. Always verify the exact model—such as GA500, GA800, A1000, V1000, HV600 or another series—against the applicable Yaskawa technical manual before changing parameters or replacing hardware. Yaskawa’s current documentation library includes separate manuals for its drive families and model-specific troubleshooting procedures.
Understanding Yaskawa AFD Faults, Alarms and Errors
Before troubleshooting a Yaskawa drive, understand what the keypad is actually telling you. A fault generally indicates a condition serious enough to stop drive operation, while an alarm or warning can indicate an abnormal condition without necessarily stopping the motor.
For example, Yaskawa documentation for the GA800 distinguishes between faults and alarms. During a fault, the keypad displays the fault code and the drive stops output; during an alarm, the alarm indication flashes and the drive will usually continue operating, although some alarms can be configured to stop the motor.
That distinction matters because repeatedly pressing RESET without correcting the underlying condition does not constitute troubleshooting. If the drive trips on overcurrent every time the motor starts, resetting it repeatedly can simply reproduce the same electrical or mechanical stress.
The basic troubleshooting sequence
A disciplined technician should work through the problem in this order:
Record the exact fault or alarm code.
Record when the fault occurs.
Determine whether it happens during startup, acceleration, steady-state operation or deceleration.
Check incoming power.
Inspect motor and output wiring.
Check the motor and driven load.
Review critical drive parameters.
Check cooling and environmental conditions.
Review fault history and monitor values.
Correct the root cause.
Reset and test under controlled conditions.
Yaskawa’s GA800 documentation specifically directs users to remove the cause of a fault or alarm before performing the fault-reset operation.
Step 1: Identify the Yaskawa Drive and Application
Do not troubleshoot a Yaskawa AFD from the fault code alone. First identify the drive family, model number, voltage class, horsepower/kW rating, motor rating and application.
Yaskawa currently provides documentation for several industrial drive families, including GA800, GA500, GA501, HV600 and iQpump605, among others. The applicable troubleshooting information depends heavily on the specific product family.
For example, a fault code may have similar terminology across multiple Yaskawa generations but different causes, parameter references or recommended corrective procedures.
Automation Pioneer also carries Yaskawa AC drives across multiple series, including GA800, HV600 and A1000 products. Yaskawa AC Drives
For replacement or application evaluation, see the Yaskawa AC Drives selection at Automation Pioneer.
Record the operating conditions
Write down:
Drive model and software/firmware information
Input voltage
Motor nameplate voltage
Motor FLA
Motor horsepower/kW
Control method
Command source
Frequency reference source
Acceleration time
Deceleration time
Motor speed when the fault occurred
Load condition
Ambient temperature
Whether the motor was starting, running or stopping
This information frequently reveals the root cause faster than the fault code itself.
Yaskawa AFD Overcurrent Fault: oC
The oC — Overcurrent fault is one of the most common Yaskawa drive faults. In Yaskawa documentation, oC is associated with excessive output current. Typical troubleshooting begins with the motor, motor load and acceleration/deceleration settings.
Common causes of oC
An overcurrent fault can result from:
Motor short circuit
Motor cable short circuit
Grounded motor conductor
Excessive mechanical load
Locked or seized motor
Acceleration time that is too short
Incorrect motor data
Incorrect control-mode configuration
Excessive starting torque demand
Motor contactor switching at the drive output
Incorrect motor connection
Damaged motor insulation
oC during acceleration
If the drive trips only while accelerating, look first at the acceleration profile and mechanical inertia.
A large conveyor, fan, pump, compressor or machine with substantial reflected inertia may require considerably more acceleration time than a lightly loaded motor.
Do not simply increase the current limit to mask the problem. First determine why the motor requires excessive torque.
oC immediately when RUN is commanded
An immediate trip points toward an electrical or parameter problem.
Inspect the motor cable for phase-to-phase and phase-to-ground faults. Check motor winding resistance and insulation resistance using procedures appropriate for the motor and drive manufacturer.
Also verify that the motor’s nameplate data has been entered correctly.
oC at low speed
Low-speed overcurrent deserves particular attention in vector-control applications. Incorrect motor data, failed auto-tuning, excessive torque demand or mechanical binding can produce high current even when shaft speed is low.
Yaskawa Overvoltage Fault: ov
The ov — Overvoltage fault occurs when the DC bus voltage rises beyond the drive’s allowable level. Yaskawa troubleshooting documentation identifies incoming voltage and deceleration time as important areas to investigate.
The most common field scenario is regenerative energy during deceleration.
When a high-inertia load decelerates, the motor can temporarily operate as a generator. That regenerated energy flows back into the drive’s DC bus. If the energy cannot be absorbed or dissipated quickly enough, DC bus voltage rises and the drive trips.
Troubleshooting Yaskawa ov
Check:
Deceleration time
Load inertia
Incoming AC voltage
Braking resistor installation
Braking resistor sizing
Braking transistor condition
Regenerative energy from the load
Mechanical braking system
Overvoltage protection settings
Increasing deceleration time is often an appropriate first diagnostic step. However, if the process requires rapid stopping, simply making the deceleration time longer may not be acceptable. In that case, the braking system needs to be evaluated.
Yaskawa documentation also identifies dynamic braking transistor and braking resistor faults as distinct conditions, reinforcing the importance of checking the complete regenerative-energy path rather than treating every ov event as an incoming-power problem.
Yaskawa Undervoltage Faults: Uv1, Uv2 and Uv3
Yaskawa uses several undervoltage-related codes.
Uv1 generally identifies DC bus undervoltage.
Uv2 identifies control-power-supply undervoltage.
Uv3 identifies a soft-charge circuit fault.
These codes appear across several Yaskawa drive documentation sets, although exact implementation varies by product family.
Troubleshooting Uv1
For Uv1, inspect the incoming electrical supply.
Check:
Line-to-line voltage
Phase balance
Fuses
Circuit breakers
Disconnects
Contactors
Loose terminals
Transformer capacity
Voltage sag during motor starts
Other large loads sharing the supply
Do not measure the supply only while the machine is idle. A voltage measurement taken during normal operation may look acceptable while the voltage collapses during acceleration or when another high-current load starts.
Troubleshooting Uv2
Uv2 points toward the drive’s control-power supply rather than simply assuming an external line-voltage problem.
Follow the model-specific Yaskawa manual and inspect the relevant control circuitry. Persistent Uv2 faults after the external supply has been verified may indicate an internal drive problem.
Troubleshooting Uv3
Uv3 is associated with the soft-charge circuit. Yaskawa documentation identifies it as a soft-charge answerback/circuit fault and, depending on the drive family, recommends power cycling and further service or replacement if the condition remains.
Yaskawa Overheat Faults: oH and oH1
A Yaskawa oH/oH1 condition indicates excessive drive temperature or heatsink temperature, depending on the drive family.
Yaskawa documentation identifies ambient temperature and cooling-fan operation as key areas to inspect for heatsink-overtemperature conditions.
Why Yaskawa drives overheat
Typical causes include:
Blocked airflow
Dirty heatsink
Failed cooling fan
High ambient temperature
Excessive carrier frequency
Drive overloaded
Incorrect drive sizing
Cabinet ventilation problems
Cabinet fan failure
Heat recirculation
Installation clearances that are too small
Start with the physical installation. A drive installed inside a hot enclosure with inadequate ventilation will eventually trip regardless of how well its parameters are programmed.
Check the cooling fan
Listen for abnormal fan noise and verify airflow.
A fan can fail intermittently, so simply observing that it spins once does not prove that it is healthy. Check whether the fan operates under the expected temperature and load conditions for the particular drive.
Check cabinet temperature
Measure the actual enclosure temperature. Do not rely solely on room temperature.
A plant floor may be at an acceptable ambient temperature while the inside of a sealed enclosure is significantly hotter because of heat generated by drives, transformers, contactors, power supplies and other equipment.
Yaskawa Motor Overload: oL1
oL1 — Motor Overload indicates that the drive has detected a motor overload condition according to its configured protection model.
Yaskawa documentation identifies load, acceleration/deceleration, cycle time and motor-rated-current settings as important troubleshooting areas.
Troubleshooting oL1
Start at the machine, not the keypad.
Ask:
Is the motor actually overloaded?
Inspect:
Conveyor material loading
Pump pressure
Fan airflow
Compressor load
Bearing condition
Gearbox condition
Misalignment
Mechanical friction
Jammed equipment
Product accumulation
Then compare measured motor current against the motor nameplate current.
If the motor is consistently operating near or above its rated current, changing the overload parameter to prevent trips is not a legitimate solution. The mechanical system, motor selection or process demand needs to be addressed.
Yaskawa Drive Overload: oL2
oL2 — Drive Overload is different from motor overload.
Here, the drive itself is being subjected to a current/load condition beyond its permissible operating profile.
Potential causes include:
Drive undersizing
Excessive load
Repeated acceleration cycles
Short acceleration/deceleration times
High starting torque
Incorrect duty classification
Excessive ambient temperature
Poor cooling
Yaskawa’s documentation specifically identifies load, acceleration/deceleration and drive rating as areas to check for oL2.
For demanding applications, verify whether the drive was selected for normal-duty or heavy-duty operation and whether the actual application matches the drive’s overload capability.
Yaskawa Ground Fault: GF
A GF — Ground Fault should be treated seriously.
Yaskawa documentation associates GF with a ground fault and recommends checking for motor or cable damage.
Potential sources include:
Damaged motor insulation
Crushed motor cable
Moisture
Contamination
Cable termination damage
Motor winding insulation failure
Incorrect wiring
Damaged output components
Before testing insulation, follow the applicable electrical safety procedure and the motor/drive manufacturer’s requirements. Do not casually megger a drive’s output terminals with the drive connected unless the manufacturer explicitly permits the procedure.
The correct approach is to isolate the drive and test the appropriate components separately.
Yaskawa Short Circuit / IGBT Fault: SC
The SC — Short Circuit/IGBT Failure indication can point toward a short circuit or failure involving the drive’s power switching section.
Yaskawa documentation identifies wiring inspection and power cycling among the troubleshooting actions; if the fault persists, drive replacement may be required depending on the model and diagnostic findings.
Before condemning the drive, verify:
Motor cable condition.
Motor insulation.
Phase-to-phase resistance.
Phase-to-ground condition.
Output wiring.
Evidence of a downstream short circuit.
If the external motor circuit checks good but the drive immediately reports an SC condition, internal power-device damage becomes a serious possibility.
Input and Output Phase-Loss Faults
Phase-loss conditions can produce unstable motor operation, excessive current and nuisance trips.
Yaskawa documentation includes PF — Input Phase Loss and LF — Output Phase Loss among its fault conditions on applicable drive families.
PF — Input Phase Loss
Check:
Incoming three-phase voltage
Fuses
Disconnect
Breakers
Contactor
Terminal connections
Supply transformer
Phase imbalance
A loose incoming terminal can create heat, voltage drop and intermittent faults.
LF — Output Phase Loss
Check:
U/V/W connections
Motor terminals
Motor cable
Output contactors
Motor winding continuity
Cable terminations
Do not place a conventional contactor between the VFD output and motor and open it while the drive is running. That can create severe electrical stress and potentially damage the drive.
Yaskawa External Faults: EF
Yaskawa drives can receive an external fault signal through digital inputs.
Depending on the drive family and configuration, codes such as EF1, EF2, EF3, EF4, EF5, EF6 and EF7 can identify external faults associated with particular input terminals. Yaskawa documentation shows these input-specific external fault codes in its drive communications and technical documentation.
The important point is that an EF fault does not necessarily mean the drive itself has failed.
Trace the signal back through the control system.
Possible sources include:
Emergency-stop circuits
Motor protection devices
PLC interlocks
Limit switches
Safety circuits
External overload relays
Pressure switches
Temperature switches
Machine permissives
Use the electrical drawings to identify exactly what device is connected to the relevant digital input.
Yaskawa Communication Faults: bUS and Related Errors
Modern Yaskawa AFDs are frequently integrated into PLC, SCADA and industrial Ethernet networks.
A communication fault can therefore originate outside the drive.
Potential causes include:
Network cable failure
Incorrect IP configuration
Node/address conflict
Communication timeout
PLC configuration problem
Option-card issue
Electrical noise
Shielding problems
Grounding problems
Incorrect communication parameters
Yaskawa documentation lists bUS — Option Communication Error among applicable drive faults.
For communication problems, troubleshoot the network systematically rather than immediately replacing the drive.
Verify physical connectivity first, then configuration, then network diagnostics, then the drive’s communication parameters.
Yaskawa Overtorque and Undertorque Detection
Yaskawa drives can also monitor torque conditions.
Codes such as oL3 and oL4 are associated with overtorque detection on applicable drive families, while UL3 and UL4 can indicate undertorque detection.
These conditions are particularly useful for process monitoring.
For example, excessive torque could indicate:
Conveyor jam
Pump blockage
Bearing failure
Mechanical interference
Product buildup
Gearbox problems
Undertorque can indicate:
Broken coupling
Pump running dry
Broken belt
Loss of mechanical load
Fan or pump operating outside expected conditions
Do not automatically disable torque detection because it is generating trips. Determine why the process torque has moved outside its expected operating envelope.
Troubleshooting a Yaskawa AFD That Will Not Run
Not every drive problem produces an obvious hardware fault.
If the keypad is powered but the motor will not run, check the command chain.
Check the run command source
Determine whether the drive expects its RUN command from:
Keypad
Digital input
PLC
Network
External controller
Then verify the configured command source.
Check the frequency reference
The drive may be receiving a RUN command but a zero-frequency reference.
Check whether the reference comes from:
Keypad
Analog input
Preset speed
PLC
EtherNet/IP
Modbus
Other fieldbus
PID controller
A common troubleshooting mistake is to focus on the motor when the actual problem is that the drive is simply receiving no valid speed reference.
Automation Pioneer maintains a broad Variable Frequency Drives category for industrial motor-control applications, including Yaskawa products and other industrial drive families.
Yaskawa AFD Fault History: Use It Before Resetting
One of the most valuable diagnostic resources is the drive’s stored fault history.
Instead of immediately clearing the fault, record the history first.
Look for patterns:
oC → oC → oC
This suggests a repeatable overcurrent condition.
oH → oH → oH
This points toward a persistent thermal problem.
Uv1 → Uv1 during large machine starts
This suggests a supply-voltage problem that may only appear under load.
ov during every rapid stop
This strongly points toward a regenerative/deceleration problem.
The sequence matters because the first visible fault may sometimes be a consequence rather than the original initiating event.
Parameter Checks That Commonly Matter
Although exact parameter numbers vary by Yaskawa family, several parameter groups deserve attention during troubleshooting.
Motor data
Verify:
Motor rated voltage
Motor rated current
Motor frequency
Motor speed
Motor power
Motor configuration
Incorrect motor data can distort current, torque and control calculations.
Acceleration and deceleration
Review these whenever you encounter:
oC
ov
oL1
oL2
The correct solution is not always to make acceleration or deceleration slower. The objective is to determine whether the selected profile matches the mechanical system.
Control mode
Verify whether the application requires:
V/f control
Open-loop vector
Closed-loop vector
Speed feedback
Torque control
PID control
A configuration intended for one control strategy may behave poorly if applied to a different motor/application combination.
Preventing Repeated Yaskawa AFD Faults
Good troubleshooting should end with prevention.
A drive that trips once may need repair. A drive that trips every week needs a system-level investigation.
Build a maintenance baseline
Record normal:
Input voltage
Output current
Motor current
DC bus voltage
Operating temperature
Frequency
Motor speed
Load condition
Then compare future measurements against the baseline.
Keep cooling systems clean
Inspect:
Fans
Filters
Heatsinks
Cabinet ventilation
Air-conditioning
Enclosure temperature
Thermal problems often develop gradually.
Inspect electrical connections
Loose power connections generate heat and voltage drop. Include drive input, motor output and control wiring in preventive-maintenance inspections.
Back up drive parameters
Maintain a documented parameter backup for critical production equipment.
When a drive fails, parameter recovery can significantly reduce commissioning time.
Yaskawa’s current GA800 documentation includes dedicated maintenance, troubleshooting and programming manuals, which makes model-specific parameter documentation an important part of a maintenance program.
Yaskawa AFD Troubleshooting Quick Reference
| Fault / Alarm | Typical Meaning | First Areas to Check |
|---|---|---|
| oC | Overcurrent | Motor, cable, load, acceleration |
| ov | Overvoltage | Deceleration, regeneration, input voltage |
| Uv1 | DC bus undervoltage | Incoming power, voltage sag, phase loss |
| Uv2 | Control power undervoltage | Control supply, internal circuitry |
| Uv3 | Soft-charge circuit fault | Soft-charge circuit, internal drive |
| oH / oH1 | Heatsink overheat | Fan, airflow, ambient temperature |
| oL1 | Motor overload | Load, motor current, motor data |
| oL2 | Drive overload | Drive sizing, load, duty cycle |
| GF | Ground fault | Motor insulation, cable, wiring |
| SC | Short circuit / IGBT failure | Motor circuit, cable, drive output |
| PF | Input phase loss | Supply, fuses, terminals |
| LF | Output phase loss | Motor cable, terminals, motor |
| EF | External fault | PLC, interlock, digital input |
| bUS | Option communication error | Network, option card, configuration |
| oL3/oL4 | Overtorque detection | Mechanical load, torque settings |
| UL3/UL4 | Undertorque detection | Load loss, belts, couplings, process |
The exact meaning and corrective procedure must always be confirmed against the manual for the particular Yaskawa drive. Similar codes appear across different Yaskawa generations, but model-specific behavior and parameter references can differ.
When a Yaskawa Drive Should Be Repaired or Replaced
A persistent fault does not automatically mean the drive should be replaced.
First eliminate external causes.
A sensible isolation process is:
Incoming power → motor cable → motor → mechanical load → control signals → parameters → drive hardware.
If the motor, cable, supply, load and configuration are verified and the same internal hardware fault repeatedly returns, the drive itself becomes the primary suspect.
Yaskawa documentation identifies situations where persistent internal faults may require drive replacement, particularly for certain soft-charge, short-circuit/IGBT and braking-related faults.
For older equipment, however, replacement decisions should also consider availability of spare parts, application criticality, downtime exposure, parameter compatibility and the possibility of upgrading to a current-generation drive.
Automation Pioneer carries legacy and current Yaskawa families, including products such as the Yaskawa V1000 Inverter and Yaskawa A1000 Inverter.
Final Yaskawa AFD Troubleshooting Checklist
When a Yaskawa AFD trips, do not start by pressing RESET.
Start by documenting the fault.
Then determine when it occurs. Startup faults, acceleration faults, running faults and deceleration faults often point toward different root causes.
Next, verify the electrical system. Check incoming voltage, phase balance, fuses, terminals, motor cable and motor condition.
After that, investigate the mechanical system. A drive is often blamed for a problem created by a seized bearing, overloaded conveyor, blocked pump, damaged gearbox or excessive machine inertia.
Finally, review the drive configuration. Motor data, acceleration/deceleration, control mode, command source and frequency reference must match the actual application.
The central principle is simple: the fault code tells you what the drive detected; it does not necessarily tell you what caused it. Effective Yaskawa AFD troubleshooting means tracing that detected condition back through the electrical, mechanical, control and environmental systems until the initiating cause is verified.
Frequently Asked Questions About Yaskawa AFD Troubleshooting
1. What is the most common Yaskawa AFD fault code?
Common Yaskawa fault conditions include oC overcurrent, ov overvoltage, Uv1 undervoltage, oH/oH1 overtemperature, oL1 motor overload, oL2 drive overload and GF ground fault. The actual frequency of each fault depends on the application and installation.
2. What does oC mean on a Yaskawa drive?
oC means overcurrent. Check the motor, motor cable, mechanical load and acceleration/deceleration profile. Yaskawa documentation specifically identifies motor, load and acceleration/deceleration as key troubleshooting areas.
3. Why does my Yaskawa drive trip on overvoltage during deceleration?
Rapid deceleration of a high-inertia load can regenerate energy back into the drive’s DC bus. Check the deceleration time, braking system, braking resistor and regenerative conditions.
4. What causes Yaskawa Uv1 undervoltage?
Uv1 indicates DC-bus undervoltage on applicable Yaskawa drives. Investigate incoming power, phase loss, voltage sag, fuses, disconnects, terminals and transformer capacity.
5. What does oL1 mean on a Yaskawa AFD?
oL1 indicates motor overload. Check actual motor current, mechanical loading, motor-rated-current configuration and acceleration/deceleration conditions.
6. What is the difference between oL1 and oL2?
oL1 relates to motor overload, while oL2 relates to drive overload on applicable Yaskawa drive families. The distinction is important because the corrective action may involve motor loading in one case and drive sizing or duty cycle in the other.
7. How do I troubleshoot a Yaskawa ground fault?
Inspect the motor and motor cable for insulation damage, short circuits, moisture and grounding problems. Isolate the drive appropriately before performing insulation tests and follow the manufacturer’s test requirements.
8. Why will my Yaskawa drive power up but not start the motor?
Check the RUN command source, frequency-reference source, digital inputs, PLC commands, interlocks, enable signals and operating limits. A powered drive does not necessarily have a valid run command or nonzero frequency reference.
9. Should I reset a Yaskawa drive immediately after a fault?
No. First identify and correct the cause. Yaskawa’s GA800 documentation instructs users to remove the cause of the fault or alarm before performing the reset operation.
10. When should a Yaskawa AFD be replaced?
Replacement becomes appropriate when external power, motor, wiring, load, control and parameter causes have been eliminated and the drive continues to exhibit a confirmed internal hardware fault. For certain persistent internal faults, Yaskawa documentation explicitly identifies replacement as a possible corrective action.
Recommended Automation Pioneer Resources
To deepen your understanding of industrial automation, critical factory infrastructure, and digital transformation, explore these related resources on Automation Pioneer:
- AC Adjustable Frequency Drives
- Yaskawa AC Adjustable Frequency Drives (AFDs)
- Yaskawa AFD Selection Guide
- Yaskawa AFD Programming & Configuration
- Yaskawa AFD Troubleshooting
- Yaskawa AFD EtherNet/IP Communication
- Yaskawa AFD Modbus Communication
- Yaskawa AFD Applications
- Yaskawa AFD vs Allen-Bradley PowerFlex
- Yaskawa AFD Installation & Wiring
- Yaskawa AFD Maintenance
These articles offer additional technical insights into the automation, networking, monitoring, and control technologies that support modern industrial automation and mission-critical infrastructure.
Check Our Comprehensive Automation Brands Get Latest Industrial Automation News
Leave a Reply