What causes FANUC alarm 331?

Part program contains an illegal G-code or M-code combination for this alarm type. Missing or incorrect address word in the program block. Axis or parameter value out of range for the commanded function. Required option not enabled on this CNC for the commanded function. Conflict between active modal states and the commanded function.

How do I fix FANUC alarm 331?

1. Note the block number shown on the alarm screen and locate that block in the program. 2. Review the command in that block against the Fanuc programming manual for alarm 331. 3. Check for missing address words, incorrect values, or conflicting G-code combinations. 4. Verify any required CNC options are enabled if using advanced functions. 5. Correct the program and verify the fix before restarting machining.

axismd.ai

FANUC Controller

Program/G-code · Intermediate · 5-30 minutes

Alarm 331

Fanuc 331 - Illegal command in peck drilling

Alarm 331 occurs when the control detects an improper command or parameter within a canned cycle peck drilling operation (G73, G83, or G87). This typically results from missing required parameters, conflicting modal commands, or illegal G-code combinations that violate the peck drilling cycle execution rules.

FANUCProgram/G-codeIntermediate5-30 minutes

331

Fanuc 331 - Illegal command in peck drilling

ILLEGAL COMMAND IN PECK DRILLING

Root Cause Summary

Alarm 331 occurs when the control detects an improper command or parameter within a canned cycle peck drilling operation (G73, G83, or G87). This typically results from missing required parameters, conflicting modal commands, or illegal G-code combinations that violate the peck drilling cycle execution rules.

Safety

Verify corrected program or parameters before resuming machining

Causes and Fixes

1
Locate the alarm line number in the program and identify the G83 or G73 block causing the alarm.
2
Verify Q value (peck increment) is present and is a positive non-zero value. Check that R-plane is above the Z-depth value.
3
Confirm all required addresses are present: X, Y (or one axis for single-axis drilling), Z (final depth), R (retract/reference plane), Q (peck depth), and F (feedrate).
4
Correct the missing or invalid parameters, ensure R > Z in negative Z drilling (R-plane must be above final depth), then reset alarm and test cycle.

Service Recommended confidence

Seeing Multiple Alarms?

Seeing another alarm with this one? Enter the code.

Get machine-aware diagnosis

AxisMD logs alarms against your actual machines, tracks patterns, and gives AI context your manual doesn't have.

Start free

Was this guide helpful?

Always verify with your machine manual or a certified technician before performing service procedures.