What causes FANUC alarm 202?

Continuous incremental moves in the same direction accumulating position beyond the register limit. Rotary axis wound multiple times in G91 incremental mode without reset. Macro or canned cycle programming error causing runaway incremental motion. Position register not reset after very long continuous axis travel in one direction. Parameter setting for axis travel range does not match actual machine capability.

How do I fix FANUC alarm 202?

1. Stop the program immediately and do not attempt to continue without resolving the position overflow. 2. Home the affected axis to re-establish a known position reference. 3. Review the program for runaway incremental moves or infinite loops causing continuous motion. 4. If using a rotary axis, add periodic position reset to prevent accumulation. 5. Check axis travel range parameters against actual machine travel limits.

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FANUC Controller

Program/G-code · Advanced · 30-90 minutes

Alarm 202

Fanuc Alarm 202 - POSITION LSI OVERFLOW

Fanuc Alarm 202 POSITION LSI OVERFLOW occurs when the position distribution pulse calculation between spindle and Z-axis exceeds the internal counter capacity during rigid tapping cycles. This typically results from incorrect rigid tapping parameters, excessively high spindle speeds relative to feed rates, or a communication error between the CNC and spindle amplifier causing position data corruption.

FANUCProgram/G-codeAdvanced30-90 minutes

202

Fanuc Alarm 202 - POSITION LSI OVERFLOW

POSITION LSI OVERFLOW

Root Cause Summary

Fanuc Alarm 202 POSITION LSI OVERFLOW occurs when the position distribution pulse calculation between spindle and Z-axis exceeds the internal counter capacity during rigid tapping cycles. This typically results from incorrect rigid tapping parameters, excessively high spindle speeds relative to feed rates, or a communication error between the CNC and spindle amplifier causing position data corruption.

Causes and Fixes

1
Navigate to SYSTEM > PARAM and verify Parameter 5200 (rigid tap mode: should be 1 for standard rigid tapping). Check Parameter 4450 (spindle gear ratio numerator) and 4451 (denominator) match your actual spindle-encoder configuration. Typical value is 1:1 for direct-drive spindles.
2
Verify the tapping program uses correct F-code format. For G84/G74 rigid tap cycles, feed rate must be calculated as F = Spindle RPM × Pitch. If F-value is extremely high or low relative to spindle speed, recalculate and modify program.
3
Check Parameter 5210 (rigid tap compensation amount) is set to default 0. Non-zero values can accumulate position errors. Also verify Parameter 5213 (tap retraction speed ratio) is between 100-300%.
4
Test with reduced spindle speed (50% of original) and proportionally reduced feedrate. If alarm clears, the original speed/feed combination exceeded LSI calculation limits. Adjust program accordingly or verify spindle max speed Parameter 3741/3742.
Always perform test tapping in air (Z clear of workpiece) when troubleshooting

DIY Feasiblemedium confidence

Call a technician if:

·Encoder replacement required
·Amplifier tuning beyond basic parameters
·Mechanical spindle repair needed
·Multiple related alarms persist

Prevention

Regular spindle bearing maintenance
Proper tap holder selection and maintenance
Conservative rigid tapping parameters for new setups
Regular encoder cable inspection

Common Mistakes

Using floating tap holders in rigid tapping
Ignoring spindle load monitoring
Incorrect encoder resolution parameters
Excessive tapping speeds for material/tap combination

Related Alarms

201 203 415 416 417

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