Yaskawa A1000 oL4 Fault — What It Means
The oL4 fault on a Yaskawa A1000 VFD indicates an overload or overtorque condition on the machine or load side of the drive output. This is not a motor thermal overload (oL1) or drive thermal overload (oL2). Instead, oL4 appears when the driven equipment is locked up, jammed, or experiencing excessive mechanical load that exceeds the torque the system can deliver.
Yaskawa’s factory guidance directs you to check the machine status and remove the cause of the fault. The fault typically points to a physical problem in the drivetrain, coupling, bearings, or driven equipment rather than an electrical issue inside the VFD itself.
Before You Replace Anything
Technicians sometimes replace the VFD power section or control boards before inspecting the mechanical load. Always verify the driven equipment turns freely by hand and check for seized bearings, broken couplings, or jammed machine components before ordering drive electronics.
Common Causes
- Mechanical jam or locked-up load (~45%) Seized bearings, obstructed conveyors, jammed pumps, or bound-up fan blades prevent the motor from turning and trigger the overload fault.
- Excessive load torque from driven equipment (~25%) The machine demands more torque than the motor and drive can supply, often due to process changes, material buildup, or worn mechanical components.
- Transmission problems (~15%) Broken couplings, seized gearboxes, damaged belts or pulleys, or binding in the drivetrain increase resistance and push torque beyond limits.
- Too-aggressive acceleration or deceleration ramp (~10%) Ramp times set too short force the drive to demand peak torque during startup or stopping, especially with high-inertia loads.
- Motor parameter mismatch (~5%) Incorrect motor nameplate data or torque-limit settings in the VFD parameters reduce available torque and make the system more sensitive to load variations.
Quick Diagnosis
Answer these to narrow it down fast.
Does the driven equipment turn freely by hand when the motor is disconnected or uncoupled?
No: A mechanical obstruction or seized component is present. Inspect bearings, couplings, belts, gears, and the driven machine for binding or damage.
Does the fault appear only during startup or rapid speed changes?
No: The fault occurs during steady running or under normal operation, pointing to a sustained mechanical overload or transmission fault.
Has the driven equipment or process changed recently (material type, product size, operating conditions)?
No: Look for wear or damage in mechanical components that have degraded over time, such as bearings, couplings, or gearboxes.
Step-by-Step Fix
- Verify the fault code in the A1000 drive history display to confirm it is truly oL4 and not oL1, oL2, or another trip code.
- Inspect the driven machine for visible obstructions, jams, or binding in conveyors, pumps, fans, compressors, or other equipment connected to the motor.
- Check mechanical transmission components including couplings, belts, pulleys, gearboxes, and reducers for signs of seizure, breakage, or excessive wear.
- Examine all bearings on the motor and driven equipment for roughness, noise, heat, or lockup by rotating the shaft by hand with power off and the load isolated.
- Remove the mechanical cause of the overload by freeing jammed parts, replacing seized bearings, repairing broken couplings, or clearing obstructions in the driven equipment.
- Review VFD parameters for correct motor nameplate data, torque-limit settings, and acceleration/deceleration ramp times to match the actual load requirements.
- Reset the fault and run the drive under controlled load conditions, monitoring torque demand and verifying smooth operation through the full speed and load range.
Parts Often Needed
| Part | Notes |
|---|---|
| Motor coupling | Amazon | If the existing coupling is broken, cracked, or shows excessive wear from overload. |
| Motor bearings | Amazon | Replace if seized, rough, noisy, or overheated; consult your motor model’s bearing spec. |
| Drive belts and pulleys | Amazon | For belt-driven systems with worn, slipping, or damaged belts that increase load torque. |
| Gearbox or reducer | Amazon | If internal gears are damaged or the unit is locked up; may require rebuild or replacement. |
When to Call a Pro
Call a qualified industrial electrician or VFD technician if you are not trained to work on high-voltage three-phase equipment or if the fault persists after you have verified the mechanical load is free and all parameters are correct. Diagnosing oL4 often requires torque monitoring, load testing under controlled conditions, and systematic parameter tuning that go beyond basic troubleshooting. If the driven equipment includes process machinery, pumps, or conveyors with complex mechanical systems, a millwright or mechanical technician may also be needed to inspect and repair transmission components safely. Always follow lockout/tagout procedures and your facility’s electrical safety practices before working on VFD-connected equipment.
Rough cost: A pro service call runs about $200-800 depending on mechanical repairs required.