When a red alarm appears on a FANUC control screen, the machine stops and the operator’s first question is always the same: what does this number mean, and how do I recover the machine as fast as possible? In this guide we group FANUC alarms by number range and cover, for each group, what it means, the most common codes and the resolution steps we actually use on the shop floor. The list is compiled from the alarm and breakdown records we have kept over years of machining.
The FANUC Alarm Map: What Each Number Range Tells You
FANUC alarm numbers are not random; the range tells you where the fault lives. The moment an alarm appears, this map tells you in seconds whether the problem is in the program, the mechanics or the electronics.
| Number range | Group | Source | First response |
|---|---|---|---|
| 000–255 | P/S (Program / Syntax) | Programming and syntax errors | Fix the program + RESET; not a machine fault |
| 300–349 | APC alarms | Absolute pulse coder / battery | Battery change; re-referencing may follow |
| 350–399 | SPC / serial encoder | Encoder communication faults | Check cables and connectors, power cycle |
| 400–499 | Servo alarms | Servo motors and drives | Check load, cables, drive LED code |
| 500–549 | OT (Overtravel) | Axis travel limit exceeded | Jog back off the limit, then RESET |
| around 700 | Overheat | Control / spindle overheating | Check fans, filters, cabinet temperature |
| 900–950 | System / hardware | Boards, RAM, CPU, fuse | Usually requires service |
P/S Alarms (000–255): Program-Related Errors
This is the group you will meet most often, and the good news is: a P/S alarm is not a machine fault — the error is in the program. Correct the code, press RESET and carry on. The examples we see most on the shop floor:
| Code | Meaning and fix |
|---|---|
| 000 | A parameter requiring power-off was entered; turn the control off and on. |
| 003 | Too many digits entered; correct the value. |
| 005 | No EOB (;) at the end of the block, or invalid data in the block. |
| 010 | An invalid G code (not available on this control) was commanded. |
| 011 | Feed (F) entered incorrectly or unsuitable for cutting. |
| 020 | In circular interpolation the start–end point difference exceeds the permitted value; check R or I/K values. |
| 029 / 030 | Offset value or offset number specified with H (T on lathes) is too large. |
| 033 | No intersection point could be computed in cutter compensation; check the contour transitions. |
| 040 / 041 | Overcutting in tool nose radius compensation; cancel with G40 in the right place and check the tool radius on small contours. |
| 059–078 | Program / sequence number not found group; check the O number and the searched N block. |
| 100 | Parameter write enabled (PWE=1). When you finish, set PWE=0 and press RESET. |
| 200–204 | Rigid tapping errors: S or F out of range, wrong M29–G84 sequencing. Check the tapping cycle blocks. |
| 224 | A move command was given before reference return; home the axes first. |
| 250 | A Z-axis move cannot be commanded in the same block as a tool change. |
For the code-by-code P/S list and detailed solutions for cycle-specific alarms (G70–G76), see our dedicated guide: FANUC P/S Alarm Codes: Common Programming Alarms.
APC and Encoder Alarms (300–399): Battery and Position Loss
On machines with absolute encoders, axis position is kept in memory by a battery while the control is off. The 300 series mostly appears when this battery weakens. The critical rule: replace the APC battery with the control switched ON; if you replace it with the power off, the position data is lost and every axis must be re-referenced. The 350 series indicates encoder communication problems — for example alarm 362 is an encoder data-transfer / timeout fault; check the cables and connectors first, then power cycle.
Servo Alarms (400–499): Motor and Drive Faults
Servo alarms concern the muscle system of the machine: motors, drives and the power/signal path between them. Before blindly power-cycling on a servo alarm, always check whether the axis is mechanically strained — a crash, packed chips, lost lubrication. More often than not the alarm is mechanics speaking, not electronics.
| Code | Meaning and fix |
|---|---|
| 400 | Servo motor or drive overload. Remove the mechanical strain, let it cool, power cycle; if it repeats, have the drive current values checked. |
| 401 | Velocity ready (VRDY) signal dropped — the drive ready signal was lost. Check drive power, the MCC contactor and the E-stop circuit; power cycle. |
| 402 / 403 | 4th-axis counterparts of alarms 400 and 401. |
| 404 | Position ready (PRDY) dropped while VRDY was on; have the control–drive signal path and boards checked. |
| 405 | Position control fault; return the axes to reference manually. |
| 408 / 409 | Spindle drive related: 408 means the spindle drive did not start correctly, 409 means an alarm is active on the drive. Read the LED / 7-segment code on the spindle drive itself and proceed from there. |
Some servo alarms are intertwined with backlash and reversal-spike problems; for the diagnosis path from workpiece marks to parameters, see our Backlash and Reversal Spike Diagnosis Guide.
Overtravel Alarms (500–549): Axis Limit Exceeded
OT alarms tell you an axis has passed its soft or hard travel limit. The remedy is the same on every axis: in JOG or HANDLE mode move the axis back in the opposite direction inside the limit, then press RESET. The numbering is systematic — the first digit encodes the axis, the last digit the direction:
| Code | Axis / Direction |
|---|---|
| 510 / 511 | X axis + / − direction limit exceeded |
| 520 / 521 | Y axis + / − direction limit exceeded |
| 530 / 531 | Z axis + / − direction limit exceeded |
| 540 / 541 | 4th axis + / − direction limit exceeded |
If an OT alarm appears during program execution, the real question is not “how do I reset it” but “why did the tool go there”: check the work offset (G54–G59) and tool length compensation before restarting the program.
System and Hardware Alarms (900–950)
This group concerns the control’s own hardware and is where operator intervention is most limited. The most valuable thing you can do is record the alarm number and the moment it occurred, and pass accurate information to service.
| Code | Meaning |
|---|---|
| 910 | Board error; have board seating and cleanliness checked. |
| 911–916 | RAM parity errors (including servo-drive and LADDER program related variants). |
| 920 | WATCHDOG alarm — a main board fault is likely. |
| 930 | CPU alarm. |
| 950 | +24V fuse in the power section blown; replace it and investigate the cause (short circuit). |
The Operator’s 5-Step Checklist When an Alarm Appears
1. Note the number and the message — before resetting. The alarm history screen keeps a record, but the live message is always more detailed. 2. Consult the map — the number range tells you whether it is program, mechanics or electronics. 3. If it is P/S, fix the program and leave the machine alone. 4. If it is servo/OT, check the mechanics first — crash, jam, travel limit. 5. If the same alarm repeats, keep a log: which program, which block, what time. Handing that log to service cuts the downtime in half. For how to use the alarm screens themselves, see FANUC Alarm, Message and Diagnosis Screens.
Frequently Asked Questions
The alarm will not clear with RESET — what now?
Some alarms (000, many servo and system alarms) clear only after a power cycle. If a power cycle does not clear it either, the cause is still active — read the message again and remove the cause; clearing the alarm does not fix the problem.
Will I lose position when changing the APC battery?
Not if you change the battery while the control is powered ON. If you change it with the power off, the absolute position is lost and the axes must be re-referenced.
Does the same number mean the same thing on every FANUC series?
The broad groups (P/S, servo, OT) work the same way across series, but individual codes can differ between series — always verify a critical alarm against your machine’s own manual. If your machine runs a Mitsubishi control, see our separate M70/M700 Alarm Codes guide.
Series guides: If your machine runs a 0i / 0i-Mate control, see our FANUC 0i / 0i-Mate Alarms page for FSSB, serial spindle and system alarm differences specific to that family; for 21i/21i-TB or 18i machines see FANUC 21i / 21i-TB Alarms.
On the operator side: For what to do about each cycle, overtravel, servo, spindle and battery alarm an operator actually meets, see our FANUC Operator Alarms page. If the alarm comes from a programming error, the FANUC G and M Code List also helps.