What causes FANUC alarm 398?

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 398?

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 398. 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.

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FANUC Controller

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

Alarm 398

Fanuc 398 - Smooth interpolation axis error

Alarm 398 occurs when the smooth interpolation (G05.1) command is programmed with an axis that is not properly configured or permitted for smooth interpolation in the control parameters. This typically happens when attempting to use smooth interpolation on a rotary axis, non-linear axis, or an axis that hasn't been enabled for AI contour control/smooth acceleration features.

FANUCProgram/G-codeIntermediate5-30 minutes

398

Fanuc 398 - Smooth interpolation axis error

SMOOTH INTERPOLATION AXIS ERROR

Root Cause Summary

Alarm 398 occurs when the smooth interpolation (G05.1) command is programmed with an axis that is not properly configured or permitted for smooth interpolation in the control parameters. This typically happens when attempting to use smooth interpolation on a rotary axis, non-linear axis, or an axis that hasn't been enabled for AI contour control/smooth acceleration features.

Safety

Verify corrected program or parameters before resuming machining

Causes and Fixes

1
Review the NC program line that triggered the alarm and identify all axes commanded in the G05.1 Q1 (smooth interpolation ON) section.
2
Check if any rotary axes (A, B, C) or non-standard axes are being interpolated while G05.1 is active.
3
Modify the program to exclude rotary/auxiliary axes from smooth interpolation blocks, or turn off G05.1 (using G05.1 Q0) before commanding those axes.
4
Verify parameters 19500-19504 (AI contour control settings) to confirm which axes are enabled for smooth interpolation if rotary axis support is required.
Modifying parameters requires proper authorization and may affect machine performance.

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