A variable frequency drive (VFD) trips for a reason. The fault code on the keypad isn’t a random inconvenience.
It’s the drive telling you exactly which parameter crossed a safety threshold in real time before something more expensive failed.
The problem is that every manufacturer labels that information differently, and a technician standing in front of a tripped drive at 2 a.m. doesn’t have time to dig through a 300-page manual.
This guide breaks down the fault codes that show up across almost every VFD brand: Allen-Bradley/Rockwell, ABB, Danfoss, Siemens, Yaskawa, and Schneider.
What actually causes them and the troubleshooting sequence that resolves them fastest.
How VFD Fault Codes Work
Every VFD continuously monitors current, voltage, temperature, and drive logic. When a measured value exceeds a programmed limit, the drive’s microprocessor interrupts output switching (usually within microseconds) and latches a fault code to protect the power module, the motor, or the mechanical load downstream.
This is different from an alarm, which is a warning that a limit is being approached but hasn’t yet forced a shutdown.
Fault codes generally fall into five categories.
- Overcurrent / short circuit faults: protect the IGBTs from instantaneous current spikes.
- Voltage faults (over/under): protect the DC bus and power supply components.
- Thermal faults: protect the drive heatsink or the motor windings
- Ground fault/earth fault: detect current leaking to the ground instead of returning through the motor circuit.
- Communication and logic faults: flag a broken link between the drive and a PLC, HMI, or fieldbus network
Common VFD Fault Codes and What They Mean
| Fault Type | Allen-Bradley (PowerFlex) | ABB (ACS series) | Danfoss (VLT/FC) | Siemens (SINAMICS) | Yaskawa (GA500/A1000) | Root Cause |
|---|---|---|---|---|---|---|
| Overcurrent | F002 / OverCurrent | 2310 OVERCURRENT | Alarm 13 | F30001 | oC | Current exceeds hardware trip limit |
| Overvoltage (DC bus) | F004 / DC Bus Overvolt | 3210 DC OVERVOLT | Alarm 7 | F30002 | oV | The motor is regenerating faster than bus can absorb |
| Undervoltage | F008 / DC Bus Undervolt | 3220 DC UNDERVOLT | Alarm 4 | F30003 | LV / Uv1 | Input power sag or phase loss |
| Ground Fault | F007 / Ground Fault | 2330 EARTH FAULT | Alarm 14 | F30021 | GF | Current path to ground, often insulation breakdown |
| Motor Overload | F007 / F122 | 2130 MOT OVERTEMP | Alarm 16 | F07011 | oL1 / oL2 | Sustained current above motor’s thermal rating |
| Drive Overtemp | F012 / Heatsink OvrTmp | 4210 IGBT OVERTEMP | Alarm 29 | F30004 | oH | Heatsink or ambient temperature too high |
| Short Circuit | F070 / Phase U/V/W Short | 2340 SHORT CIRCUIT | Alarm 16 | F30022 | SC | Direct phase-to-phase or phase-to-ground short |
| Input Phase Loss | F003 / Input Phase Loss | — | Alarm 33 | F30011 | PF | One incoming supply phase missing or unbalanced |
| Output Phase Loss | F005 / Output Phase Loss | 2312 | Alarm 30 | F30012 | LF | Open motor lead or motor winding failure |
| Comm Fault | F081 / Comm Loss | — | Alarm 46 | F08501 | CE | Lost link to PLC/HMI/fieldbus |
Exact codes vary by firmware version. Always confirm against your specific drive’s fault table, but the underlying causes below apply almost universally.
How to Fix Each VFD Fault
Overcurrent Fault
This is the most frequent VFD trip, and it’s rarely the drive itself that’s at fault.
- Check for a mechanical jam, seized bearing, or blocked fan/pump impeller that’s forcing the motor to draw excess current on startup
- Verify the drive’s acceleration ramp isn’t too aggressive for the load’s inertia. A load that can’t spin up fast enough pulls current the drive interprets as a fault
- Confirm motor nameplate current matches the drive’s motor parameter settings; an undersized motor parameter will trip on normal load current
- Inspect motor cabling for a phase-to-phase short or damaged insulation using a megohmmeter
Overvoltage Fault (DC Bus)
Overvoltage almost always happens during deceleration, when a spinning motor with high inertia feeds energy back into the drive faster than the DC bus can dissipate it.
- Extend the deceleration time (ramp-down) so the load slows more gradually.
- Add or verify a braking resistor and confirm the dynamic braking parameter is enabled.
- Check incoming line voltage isn’t running high, especially on lightly loaded three-phase feeders.
- For fan and pump loads, enable the drive’s built-in flying-start or ride-through function instead of a hard stop.
Undervoltage Fault
- Measure incoming supply voltage under load; a sagging feeder, undersized transformer, or long conductor run causes voltage drop.
- Check for a loose or corroded terminal connection on the input side.
- Look for other large loads (welders, compressors) starting on the same circuit and dragging voltage down momentarily.
- If undervoltage trips correlate with utility events, consider a line reactor or UPS on the control power.
Ground Fault
- Disconnect the motor and megger each phase to ground; a reading under 1 MΩ generally indicates winding insulation breakdown.
- Inspect motor cable for chafed insulation where it passes through conduit fittings or panel knockouts.
- Check for moisture intrusion in the motor junction box, especially on outdoor or washdown applications.
- Rule out the drive itself by testing with a known-good motor if the fault persists with everything else isolated.
Motor Overload / Thermal Fault
- Confirm the motor’s full-load amps (FLA) match what’s programmed in the drive’s motor overload parameter.
- Check for a mechanical binding condition making the motor work harder than the process requires.
- Verify motor cooling isn’t obstructed. A dirty or blocked motor fan shroud raises winding temperature under normal current.
- On variable torque loads at low speed, confirm the motor is rated for the reduced cooling that comes with low-speed continuous operation.
Drive Overtemperature
- Check that the panel or enclosure ventilation is functioning. A failed enclosure fan is one of the most common causes.
- Clean the drive’s heatsink fins and internal fan; dust buildup is a frequent culprit in industrial environments.
- Confirm ambient temperature around the drive is within the manufacturer’s rated range.
- Verify the drive isn’t derated for altitude or enclosure type but is installed without accounting for that derating.
Phase Loss (Input or Output)
- For input phase loss, check upstream fuses, circuit breakers, and contactor contacts for one open leg.
- For output phase loss, check motor cable continuity conductor-by-conductor and inspect the motor terminal box.
- Measure phase-to-phase voltage balance; more than a 2% imbalance across phases warrants investigation upstream.
Communication Fault
- Verify network cabling, terminating resistors, and grounding on the fieldbus (Modbus, EtherNet/IP, Profinet, etc.).
- Confirm the drive’s node address or IP configuration matches what the PLC program expects.
- Check for electrical noise coupling into communication cable runs routed alongside motor power cables.
- Reset the drive’s communication watchdog timeout if brief PLC scan delays are triggering nuisance trips.
General Troubleshooting Sequence
When you don’t yet know which category a fault falls into, work through it in this order:
- Record the exact fault code and any fault history log before clearing it. Most drives store the last several faults with timestamps, which helps spot patterns.
- Check drive status LEDs and display for supplementary alarm codes that may have preceded the trip.
- Isolate the motor from the drive and test motor insulation resistance and winding continuity independently.
- Verify incoming power quality, voltage, phase balance, and frequency before assuming the drive itself has failed.
- Review recent changes. A fault appearing right after a parameter change, firmware update, or mechanical modification points straight to the cause.
- Clear the fault and monitor drive parameters (current, DC bus voltage, temperature) in real time on the next run if the drive supports live monitoring.
Preventing Repeat VFD Faults
Most recurring VFD faults trace back to preventable maintenance gaps rather than drive defects.
- Keep enclosure filters and drive heatsinks clean on a scheduled interval, not reactively
- Torque-check power terminals annually. Loose connections cause both overcurrent and overtemperature faults.
- Re-verify motor parameters any time a motor is swapped or rewound.
- Log fault history over time; a drive that faults intermittently under the same conditions usually has a mechanical or electrical root cause, not a drive defect.
FAQ
What does it mean when a VFD keeps faulting after a reset?
A fault that returns immediately after reset almost always indicates the underlying condition (short circuit, ground fault, or blocked mechanical load) is still present rather than being a nuisance trip. Don’t keep resetting and running. Isolate the cause first.
Can a bad VFD fault code damage the motor?
The fault code itself is a protective response, not the cause of damage. The condition that triggers it, sustained overcurrent, ground fault, or overtemperature, is what can damage windings if the drive doesn’t trip in time or if faults are repeatedly forced past their protective limit.
Is an overvoltage fault the drive’s fault or the motor’s?
Neither, usually. Overvoltage is almost always caused by regenerative energy during deceleration exceeding what the DC bus and braking system can absorb, a ramp-time or braking-resistor sizing issue, not a component failure.
Do all VFD brands use the same fault code numbers?
No. Fault code numbering is brand- and firmware-specific, though the underlying fault categories (overcurrent, overvoltage, ground fault, overload, thermal) are standard across the industry. Always cross-reference the specific drive’s fault table.