FANUC Alarm Codes: Complete Troubleshooting Guide

By Nishikant Xalxo | CNC Troubleshooting Expert | Updated: January 10, 2025 | 10 min read

After 6 years running FANUC 0i-MF and 30i-B controls, I've seen every alarm in the book. Here's how to fix them without calling the service department (most of the time).

Understanding FANUC Alarm Structure

FANUC alarms follow this pattern: ALARM TYPE + NUMBER

Common PS Alarms (Program Errors)

PS0001: ILLEGAL CODE

The program contains an unrecognized character or syntax error.

Solution:
  1. Check for missing semicolons at block ends
  2. Look for lowercase letters (FANUC only accepts uppercase)
  3. Verify special characters like parentheses are closed
PS0041: ILLEGAL CUTTER COMP

Cutter compensation start or cancel is incorrect.

Solution:

Always move linearly (G01) into cutter comp, never rapid (G00). Lead-in distance must be > tool radius.

Correct: G01 G41 D01 X10.0 F20.0
Wrong:   G00 G41 D01 X10.0      (causes alarm)
PS0120: ILLEGAL OFFSET VALUE

Tool offset register contains invalid data.

Solution:

Check offset page for negative values in diameter offsets (should be positive). Verify tool numbers match program.

OT Alarms (Over-Travel)

OT0500/+: OVERTRAVEL

Axis has exceeded soft limit during movement.

Solution:
  1. Press RESET to clear alarm
  2. Jog axis manually away from limit
  3. Check program for incorrect coordinates
  4. Verify work offset (G54) is set correctly

Tip: Use G53 G00 Z0 to send Z to machine zero before M30 to avoid OT alarms.

SV Alarms (Servo Errors)

SV0401: SERVO V-READY OFF

Servo drive is not ready. Common after emergency stop.

Solution:
  1. Release E-stop button
  2. Press RESET and wait 10 seconds
  3. If persists, check servo drive power indicators
  4. Cycle machine power if needed
SV0436: SOFT THERMAL (OVH)

Servo motor overheating due to continuous operation.

Solution:

Stop program. Let motor cool for 15-20 minutes. Reduce feed rates or add dwells in program. Check for mechanical binding.

SP Alarms (Spindle Errors)

SP1220: NO SPINDER AMP

Spindle amplifier not communicating. Common after power glitch.

Solution:
  1. Check spindle amplifier LED status
  2. Cycle machine power
  3. Verify parameters 3701-3704 are correct
  4. Check cable connections to spindle drive

Resetting Alarms

Procedure:

  1. Press RESET button
  2. If alarm remains, check alarm history on POS screen
  3. For servo/spindle alarms, may need to cycle power
  4. Document alarm number before resetting for service reports
About the Author: Nishikant Xalxo has cleared thousands of FANUC alarms without service calls. He teaches alarm troubleshooting to new operators at his shop. Questions? nxdecore@gmail.com

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