Cooling fan
Common VFD, drive, UPS, and cabinet overheating failure point.
Fanuc Alarm 500 — What It Means
Fanuc Alarm 500 is an overtravel alarm — one or more axes traveled beyond the software overtravel limits stored in the machine parameters. Unlike hardware overtravel alarms (1-4 series), Alarm 500 is a software position check; the control detected that the commanded path would enter or has entered the software travel boundary.
Common Causes
- Machine returned to wrong reference position — After a power cycle or battery change, if the reference return wasn’t completed correctly, the machine’s position understanding is wrong and normal moves trigger 500.
- Part offset or work coordinate set incorrectly — A work coordinate (G54-G59) or tool length offset that positions the program path outside the machine travel envelope triggers 500.
- Program error — A G-code program commanding a position beyond the machine’s soft limits triggers 500 before the move executes.
- Soft limit parameter changed — Incorrect or reduced travel limits in machine parameters cause normal positions to trigger Alarm 500.
Step-by-Step Fix
- Identify which axis triggered 500 — The Fanuc alarm display shows the axis designation. Note it.
- Check current position vs. soft limits — On the Fanuc position display, compare the current machine coordinate to the soft limit values in parameters (typically P1320/P1321 for positive/negative limits per axis).
- Re-execute reference return — If position is uncertain after a power cycle, execute ZRN (reference return) on all axes before any other motion.
- Check work coordinates and offsets — Verify G54 (or active work coordinate) and tool length offsets are correct for the current setup.
- Manual jog out of limit — If the axis is inside the soft limit boundary, use the [OVR cancel] function (hold RESET and press the positive or negative axis jog button on some Fanuc versions) to jog out of the soft limit zone.
Parts Often Needed
| Part | Notes |
|---|---|
| Backup battery | If position was lost due to battery failure |
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 Alarm 500 triggers on moves that were previously fine, a parameter change or position calibration issue needs Fanuc-certified service to diagnose.