Fanuc Alarm 500 and 501 (Overtravel): What They Mean and How to Recover

Key Takeaways: Fanuc alarms 500 and 501 are stored-stroke overtravel alarms: the axis crossed its software travel limit in the plus direction (500) or minus direction (501). The machine is protecting itself from running an axis past its safe envelope. Recovery is usually simple, jog the axis back inside the limit, but repeat overtravels almost always trace to a work offset, tool offset, or program error worth fixing at the source.

What alarms 500 and 501 mean

Fanuc controls maintain software stroke limits per axis (commonly set in parameters 1320 for the plus limit and 1321 for the minus limit). Alarm 500 reads "OVER TRAVEL: +n" and alarm 501 reads "OVER TRAVEL: -n", where n is the axis. The control stops the axis the moment its commanded or actual position crosses the stored limit.

These are among the most benign Fanuc alarms when they happen once, and among the most telling when they repeat: something is sending the axis somewhere it should not go.

How to recover safely

• 1. Identify direction and axis from the alarm text (for example, +X means the X axis tripped its plus limit).
• 2. Switch to jog or handle mode.
• 3. Move the axis in the OPPOSITE direction of the trip, back inside the travel envelope. The control allows motion away from the violated limit.
• 4. Reset the alarm. On many machines the alarm clears with the reset key once the axis is back inside limits.
• 5. If the machine tripped a HARD overtravel switch (physical limit switch, not just the soft limit), most builders provide an overtravel release button that must be held while jogging off the switch. Move slowly and only in the escape direction.

If the alarm appears immediately at power-up far from any physical limit, the machine may have lost its reference position, which is a different problem: see our guide to the Fanuc APC alarm 300 battery and zero-return issue.

Why it happened: find the source

• Wrong work offset (G54-G59). The most common cause on machining centers: an offset entered for a different fixture sends a rapid move past the limit.
• Wrong tool length offset. Especially on Z-axis overtravels near toolchange or first approach.
• Program error. A missing decimal point or a coordinate in the wrong system (G90 vs G91 mixups are classic).
• Manual jog inattention at high jog rates near the envelope edge.
• Changed soft-limit parameters after service work, tighter than the program assumes.

Preventing repeats

Log each overtravel with its axis, direction, program, and operator note in your CMMS: three overtravels on the same program in a month is a program or setup problem with a name on it. Verify offsets against a first-piece checklist, and dry-run new programs with rapid override down. On the analytics side, overtravel stops are exactly the kind of short interruption that manual logs miss: Fabrico's computer-vision-verified OEE records every stop with its true duration, so downtime analysis shows how much these small events actually cost.

FAQ

The axis will not move in either direction. What now?
Check whether a hard limit switch tripped and use the machine builder's overtravel release procedure. If the control blocks both directions on a soft limit only, verify you are jogging the correct axis and mode.

Can I widen the soft limits in parameters 1320/1321?
Only to match the machine's real mechanical envelope, per the builder's documentation. Widening limits to silence an alarm invites a hard crash.

Why does it overtravel only on one specific part program?
Almost certainly an offset or coordinate in that program. Compare the commanded end points against the machine envelope before blaming the machine.

To see how automatic stop capture turns small recurring alarms into visible, fixable patterns, book a demo.