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Fanuc 0i-MD Alarm Codes — What They Mean
The Fanuc 0i-MD is a common machining center control used on vertical mills, horizontal machining centers, and compact CNC machines. Fanuc alarms are numeric and can come from the CNC, PMC, servo system, spindle drive, or ladder logic. The first job is to identify whether the alarm is a program issue, a motion issue, or a hardware issue.
Fanuc 0i-MD Common Alarm Reference
| Alarm | Meaning |
|---|---|
| 000 | General reset / no alarm |
| 100 | Parameter error |
| 300 | Emergency stop |
| 401 | Servo alarm — VRDY off |
| 414 | Digital servo system alarm |
| 424 | Overtravel + direction |
| 430 | Stored stroke limit 1 |
| 500 | Overcurrent in servo amplifier |
| 700 | Spindle alarm |
| 750 | Serial pulse coder fault |
| 910 | SRAM parity error |
Common Causes by Alarm
- 300 E-stop — Physical E-stop pressed, broken E-stop chain, or door interlock open.
- 401 / 414 servo alarms — Servo amplifier not ready, axis overload, encoder issue, or amplifier power supply fault.
- 424 overtravel — Axis hit travel limit switch or parameterized soft limit.
- 500 servo overcurrent — Axis jammed, ballscrew binding, or amplifier fault.
- 750 pulse coder — Encoder cable loose, contaminated connector, or failed encoder battery causing reference loss.
Step-by-Step Fix
- Read the exact alarm screen — Fanuc often gives additional text beyond the number.
- Check alarm source — CNC screen, servo amplifier LEDs, and spindle amplifier LEDs should all be reviewed.
- For 300 — Verify all E-stop buttons, door switches, and safety relays are reset.
- For 424 — Jog off the limit if mechanically possible, then inspect the limit switch and home reference.
- For 750 — Check encoder battery voltage and cable seating before replacing hardware.
Parts Often Needed
| Part | Notes |
|---|---|
| Encoder battery | Common maintenance item on Fanuc controls |
| Pulse coder cable | Replace if oil-soaked or damaged |
| Limit switch | For repeated overtravel alarms |
| Servo amplifier | For persistent 401/500 alarms |
Technician Tips
CNC alarms should always be diagnosed by reading the full alarm text, not just the number. Modern Fanuc, Haas, and Mazak controls provide detailed alarm descriptions — press the help key while viewing the alarm for diagnostic suggestions. The alarm history screen stores the last 50-100 alarms with timestamps; review this before clearing to identify patterns. A servo alarm (SV series on Fanuc) that appears only during rapid traverse points to a different cause than one that appears during cutting.
Prevention: Back up your CNC parameters monthly. Battery-backed memory faults are much easier to recover when you have a current parameter, ladder, offset, and macro backup. Replace control batteries on a planned maintenance schedule before voltage drops far enough to risk data loss.
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.
When to Call a Pro
If the machine shows repeated 910 SRAM or persistent servo amplifier alarms after basic checks, back up parameters immediately and involve a Fanuc service technician or qualified CNC controls specialist.