Cooling fan
Common VFD, drive, UPS, and cabinet overheating failure point.
Fanuc Soft OT Alarm
A Fanuc soft OT alarm means the axis exceeded a software-defined travel limit. This is different from a hard overtravel where a physical limit switch is hit. The control stopped motion because the machine position exceeded parameter limits.
Common Causes
| Cause | Details |
|---|---|
| Wrong work offset | Program zero shifted too far |
| Machine lost reference return | Absolute position no longer valid |
| Travel limit parameters wrong | After battery loss or bad restore |
| Manual jog past software limit | Common during setup |
How to Clear It
- Put the machine in JOG or HANDLE mode
- Use overtravel cancel / OT release if your machine builder provides it
- Jog the axis back toward the safe travel area
- Re-reference the machine
- Check offsets and parameters before restarting the job
Soft OT vs. Hard OT
| Type | Meaning |
|---|---|
| Soft OT | Control/calculated limit exceeded |
| Hard OT | Physical limit switch activated |
Technician Tips
Fanuc CNC alarms use a prefix system that tells you where the fault lives: SV = servo, SP = spindle, PS = PMC/PLC, OT = overtravel. SV041 (position error too large) is the most common servo alarm — check the servo amplifier LED before replacing the motor or encoder. If the amplifier shows a ”—” or blank display, the issue is likely the power supply to the amplifier. If the display is normal, use the servo monitor screen (function key + SV toggles) to check actual vs commanded position. A 0.1mm following error at rest is normal; anything over 0.5mm at standstill means the axis is drifting.
Cost guide: Fanuc servo amplifier replacement runs $2,000-$4,000. Encoder cable replacement: $200-$400. Always try cable reseating first — it fixes about 30% of SV alarms.
Need Replacement Parts?
Before ordering, match the machine-control part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
If the alarm clears once the axis is moved back and the machine is re-homed, it was likely a true soft overtravel. If it remains, check limit switches, parameters, and absolute position status.
Bottom Line
Fanuc soft OT alarms are usually caused by bad position data or bad setup data, not failed hardware. Back off the axis safely, re-home, and verify your work offsets.