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Access Siemens HMI > Diagnostics > Machine Data (MD) menu. Navigate to MD 32100 and verify TOOL_CHANGER_TYPE is set to a valid value (0=no changer, 1=ATC, 2=manual, etc.). Document the current setting.

Do not modify MD values without supervisor authorization; changes require a machine restart.

Check MD 32110 (TOOL_HOLDER_NUM) to confirm the spindle/tool holder number matches the T-word value in the NC program and the physical tool changer configuration. Cross-reference against your tool changer documentation for valid holder IDs.

Verify MD 32120 (SPINDLE_NO) and MD 32130 (SPINDLE_OFFSET) are defined and correspond to the spindle used for tool changes. On multi-spindle machines, ensure the correct spindle index is referenced.

If parameters are undefined or zero, set them to match your tool changer configuration per the machine builder's documentation, then perform a warm restart (Siemens HMI > System > Restart).

Review the NC program block that triggered the alarm (shown as block %2 in the alarm message). Identify the T-word value and M6 command, and note the requested tool holder/spindle number.

Cross-check the requested tool holder number against MD 32110 and the valid range defined in MD 32100. Consult your tool changer capacity documentation (e.g., slots 1-24 for ATC, or spindle indices 1-4 for multi-spindle).

If the T-word exceeds the configured tool holder range, either correct the NC program to use valid tool numbers or extend the tool holder configuration in machine data (requires approval and restart).

Test with a simple program (e.g., T1 M6) to verify the tool changer responds. Monitor the PLC interface variables (Tool Holder Status inputs) via Diagnostics > PLC > Inputs to confirm the tool changer acknowledges the request.

Access Siemens HMI > Diagnostics > PLC > Inputs/Outputs. Locate the tool changer control signals (typically named Tool_Changer_Request, Tool_Holder_Ready, Tool_Change_Complete). Verify these signals exist and are not stuck at an invalid state (e.g., all zeros or permanently high).

Do not force PLC signals unless under controlled conditions with the spindle stopped and machine secured.

Review the PLC program source code (Siemens HMI > Program > OB1 or tool change subroutine). Confirm the M6 handler contains logic that reads tool holder feedback and writes the tool changer enable/select outputs. Check that the logic respects the spindle/holder number from MD 32110.

Verify MD 32105 (TOOL_CHANGER_IO_MODULE) and MD 32106 (TOOL_CHANGER_IO_OFFSET) point to the correct I/O module and address range where the tool changer signals are wired. Cross-reference the machine documentation and electrical schematics.