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FANUC Controller
Tool Changer · Intermediate · 5-30 minutes
Fanuc 257 - Tool change command error
Alarm 257 occurs when the control detects an improper tool change command in the part program. This is typically caused by incorrect M-code formatting, attempting tool changes during invalid machine states, or sequencing errors in the tool change macro.
257
Fanuc 257 - Tool change command error
TOOL CHANGE COMMAND ERROR
Fanuc PS program alarm 257: TOOL CHANGE COMMAND ERROR. This alarm is triggered by an illegal or incorrectly formatted command in the part program, or a programming condition that the Fanuc control cannot execute.
Root Cause Summary
Alarm 257 occurs when the control detects an improper tool change command in the part program. This is typically caused by incorrect M-code formatting, attempting tool changes during invalid machine states, or sequencing errors in the tool change macro.
Safety
- Verify corrected program or parameters before resuming machining
Causes and Fixes
- 1
Review the program line causing the alarm and verify the tool change format matches your machine specification (e.g., T01 M06 or M06 T01).
- 2
Check that the tool number is within valid range (typically T01-T99 or higher depending on magazine capacity) and exists in the tool table.
- 3
Verify there are no missing or extra characters in the tool change block (spaces, decimal points, or letters where numbers should be).
- 4
Test with a simple manual tool change command from MDI to confirm proper syntax for your specific machine configuration.
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