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. Parameter loss from dead batteries is the #2 cause of unexpected CNC downtime (after mechanical crashes). Replace control batteries annually before they fail.
Need Replacement Parts?
Finding the right replacement parts for your equipment is critical to getting it running again. 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.