What causes FANUC alarm PS042?

Part program contains an illegal or incorrectly formatted command for this alarm type. Missing required address word or parameter value in the program block. Programmed value is outside the allowable range for this function. Conflict between the commanded function and the current modal state. Program post-processor not configured correctly for this Fanuc series.

How do I fix FANUC alarm PS042?

1. Note the block number from the Fanuc alarm screen and locate it in the program. 2. Review the command in that block against the Fanuc programming manual for alarm PS042. 3. Check for missing address words, incorrect values, or conflicting G-code combinations. 4. Verify any required machine options are enabled if using advanced functions. 5. Correct the program and verify before resuming machining.

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FANUC Controller

Program/G-code · Basic · 10-15 minutes

Alarm PS042

Fanuc Alarm PS042 - Invalid M Code

Fanuc PS042 Invalid M Code alarm occurs when the control encounters an M-code that is undefined in the M-code table, exceeds the allowable M-code range defined in parameters, or violates execution conditions such as attempting to execute an M-code blocked by parameter settings or modal restrictions. This alarm typically relates to PMC ladder logic configuration, M-code parameter definitions in the 3000 series, or syntax errors in the part program.

FANUCProgram/G-codeBasic10-15 minutes

PS042

Fanuc Alarm PS042 - Invalid M Code

G45/G48 NOT ALLOWED IN CRC

Root Cause Summary

Fanuc PS042 Invalid M Code alarm occurs when the control encounters an M-code that is undefined in the M-code table, exceeds the allowable M-code range defined in parameters, or violates execution conditions such as attempting to execute an M-code blocked by parameter settings or modal restrictions. This alarm typically relates to PMC ladder logic configuration, M-code parameter definitions in the 3000 series, or syntax errors in the part program.

Safety

Unknown M codes may cause issues

Causes and Fixes

1
Navigate to SYSTEM > PARAM and check parameter 3000 to verify the maximum M-code number allowed (typically 99 or 255 depending on control series).
2
Review parameters 3001-3032 to confirm the offending M-code is defined with a valid PMC address assignment (G address format: G##.#). Each parameter defines one M-code decode address.
3
Check the part program at the alarm line for the M-code value. If M-code exceeds parameter 3000 setting or is not listed in 3001-3032, either add the M-code definition to an available parameter slot or correct the program.
Modifying M-code parameters requires PMC ladder logic verification to ensure proper signal handling
4
If adding new M-code definitions, verify PMC ladder has appropriate logic at the assigned G address to handle the M-code completion signal (FIN) back to CNC.

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