What causes FANUC alarm 237?

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 237?

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 237. 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 237

Fanuc 237 - Illegal command in gentle start

Alarm 237 occurs when the CNC detects an incompatible or illegal G-code command during the gentle start (soft start) acceleration phase. Gentle start is a special motion control feature that requires specific motion commands, and certain G-codes, auxiliary functions, or parameter changes are not permitted during this phase. This typically happens when M-codes, tool changes, or non-motion commands are programmed during gentle start acceleration or deceleration blocks.

FANUCProgram/G-codeIntermediate5-30 minutes

237

Fanuc 237 - Illegal command in gentle start

ILLEGAL COMMAND IN GENTLE START

Root Cause Summary

Alarm 237 occurs when the CNC detects an incompatible or illegal G-code command during the gentle start (soft start) acceleration phase. Gentle start is a special motion control feature that requires specific motion commands, and certain G-codes, auxiliary functions, or parameter changes are not permitted during this phase. This typically happens when M-codes, tool changes, or non-motion commands are programmed during gentle start acceleration or deceleration blocks.

Safety

Verify corrected program or parameters before resuming machining

Causes and Fixes

1
Review the program block where the alarm occurred and identify any M-codes, T-codes, S-codes, or H/D offset changes in the gentle start section.
2
Move all auxiliary functions (M-codes, tool changes, spindle commands) to separate blocks before or after the gentle start motion blocks.
3
Verify gentle start parameters (typically 1620-1625) are properly configured and check parameter 1620 bit settings for enabled gentle start axes.
Modifying parameters requires proper authorization and documentation.
4
Test the modified program in single block mode to confirm smooth execution through the gentle start zone without alarm recurrence.

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