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Review the main program and identify all M98 subprogram call sequences. Count the maximum nesting depth (subprograms calling other subprograms).

Check control parameter documentation for maximum allowed nesting levels (typically 4 levels on older controls, 8+ on newer models).

Restructure the program to reduce nesting depth by consolidating subprograms or using sequential calls instead of nested calls.

Back up all programs before modification

Test modified program in single block mode to verify alarm is cleared and machining sequence is correct.

Search all programs for recursive calls where a subprogram number appears in both the program name (Oxxxx) and within an M98 call in the same program.

Review macro programs (G65/G66) for conditional statements (IF/WHILE/GOTO) that may create unintended loops without proper exit conditions.

Trace the call sequence through all nested programs to identify circular call patterns (e.g., O1000 calls O2000, which calls O3000, which calls O1000).

Correct the logic error by removing recursive calls or adding proper exit conditions with M99 or GOTO statements with loop counters.

Ensure loop counters are properly incremented and tested

Examine the program for nested WHILE loops, especially WHILE-DO-END structures within macro programs that also call subprograms.

Check for G66 modal macro calls combined with M98 subprogram calls, as both consume stack levels simultaneously during execution.

Simplify macro logic by breaking complex nested structures into sequential operations or separate macro programs called at the same level.

Verify variable passing between modified macros maintains correct values

If simplification is not possible, consult Fanuc documentation for parameter settings that may increase stack depth (control model dependent), or consider upgrading control memory.

Parameter changes require proper authorization and documentation