What causes FANUC alarm PS021?

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 PS021?

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 PS021. 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 · Intermediate · 10 minutes

Alarm PS021

Fanuc Alarm PS021 - Wrong Plane Selection

PS021 alarm occurs when the CNC detects a commanded axis movement that is incompatible with the currently active plane selection (G17/G18/G19) during circular interpolation (G02/G03) or canned cycle execution. The control expects axis assignments to match the plane definition: G17 (XY), G18 (ZX), or G19 (YZ), and rejects commands that violate this geometric relationship.

FANUCProgram/G-codeIntermediate10 minutes

PS021

Fanuc Alarm PS021 - Wrong Plane Selection

ILLEGAL PLANE SELECT

Root Cause Summary

PS021 alarm occurs when the CNC detects a commanded axis movement that is incompatible with the currently active plane selection (G17/G18/G19) during circular interpolation (G02/G03) or canned cycle execution. The control expects axis assignments to match the plane definition: G17 (XY), G18 (ZX), or G19 (YZ), and rejects commands that violate this geometric relationship.

Safety

Verify plane selection before arcs

Causes and Fixes

1
Review program block causing alarm. Verify plane selection code (G17 for XY, G18 for ZX, G19 for YZ) matches the axes used in subsequent G02/G03 circular commands. Check O-number program line number displayed with PS021 alarm on ALARM screen.
2
Examine I/J/K arc center designations in circular interpolation block. G17 plane requires I and J only, G18 plane requires I and K only, G19 plane requires J and K only. Verify no conflicting axis letters are programmed.
3
Check parameter 1022 (Input Unit) to verify coordinate system interpretation matches program expectations. Navigate SYSTEM > PARAM > search 1022. Confirm metric (bit assignment) or inch settings align with G-code.
4
Correct program by either changing plane selection G-code to match intended arc plane or modifying circular interpolation command to use correct axis pairs and I/J/K designators for active plane.

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