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Fanuc Alarm 5 — What It Means
Fanuc alarm 5 indicates a stored stroke limit 2 overtravel. This is similar to alarm 4 but references the second set of stored stroke limits, which is used to define an inner forbidden zone or a secondary travel boundary on Fanuc Series 0, 10, 11, 15, 16, 18, 21, and 0i controls. Stroke limit 2 is typically set to protect the machine spindle head from colliding with the table or pallet in a specific zone during tool change or pallet exchange operations.
Common Causes
- Tool change or ATC sequence positioned axis into forbidden zone — An automatic tool changer or pallet changer commanded an axis move into the zone protected by stroke limit 2.
- Incorrect stroke limit 2 parameters — Parameters P1322/P1323 (or equivalent for the control series) define the stroke limit 2 boundaries and may be configured incorrectly after a machine parameter backup/restore.
- Machine not properly referenced after E-stop — If the control lost the reference position, it cannot correctly enforce the stroke limit 2 boundaries and may trip prematurely.
- MDI or program move into the protected zone — A commanded position entered manually or by the NC program entered the area defined by stroke limit 2.
Step-by-Step Fix
- Jog the axis away from the overtravel position — Switch to Jog or MPG mode. Move the affected axis in the opposite direction from the limit that was exceeded. The alarm typically clears once the axis re-enters the valid zone.
- Check which stroke limit zone is active — On the Fanuc diagnosis screen or the position display, check the current axis position against the stroke limit 2 parameters to understand which boundary was crossed.
- Perform a zero return — After recovering the axis, execute a reference return (REF mode or G28 in MDI) to re-establish the machine zero reference point.
- Review parameters for stroke limit 2 — Navigate to the parameter pages and check P1322 and P1323 for the relevant axis. Confirm these correctly define the forbidden zone for your machine configuration.
- Review the ATC or pallet change sequence — If the alarm occurred during an automatic operation, check the macro or ATC sequence logic for a command that moves the axis into the forbidden zone.
- Correct the NC program — If a program move caused the alarm, edit the program to avoid the protected zone or adjust the stroke limit 2 boundaries to correctly reflect the machine’s geometry.
- Reset and test — Reset the alarm with the Reset key and run a test cycle to confirm alarm 5 does not recur.
Parts Often Needed
| Part | Notes |
|---|---|
| No parts typically required | Alarm 5 is a software boundary fault; recovery is via parameter or program correction |
| Fanuc servo drive or motor | Only if position feedback error caused the axis to appear outside limits |
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 5 occurs in positions that appear to be within the expected travel range, the position feedback system (encoder, linear scale) may be reporting incorrect axis position. Contact a Fanuc-certified technician for encoder and servo drive verification.