What causes FANUC alarm 090?

Machine powered on but reference return not performed before attempting to run a program. Reference return was interrupted or did not complete successfully on all axes. Program uses absolute coordinates but reference has not been established. Parameter enables reference return check and the axis did not complete homing. Emergency stop or power failure occurred during reference return leaving axes in an undefined state.

How do I fix FANUC alarm 090?

1. Perform a reference return (home) on all axes before running the program. 2. Ensure all axes complete their reference return — check each axis reaches the home position indicator. 3. If reference return was interrupted, repeat from the beginning for all axes. 4. Check for any axis-specific alarms that may have prevented homing from completing. 5. Verify the reference return parameters are correct if homing does not complete normally.

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FANUC Controller

Program/G-code · Intermediate · 15-30 minutes

Alarm 090

Fanuc Alarm 090 - REFERENCE RETURN INCOMPLETE

Fanuc Alarm 090 occurs when the CNC detects that one or more axes failed to complete the reference point return sequence properly. This is typically caused by incorrect reference point parameters, position coder/encoder issues, dog switch problems, or mechanical interference preventing the axis from reaching the grid reference position.

FANUCProgram/G-codeIntermediate15-30 minutes

090

Fanuc Alarm 090 - REFERENCE RETURN INCOMPLETE

REFERENCE RETURN INCOMPLETE

Root Cause Summary

Fanuc Alarm 090 occurs when the CNC detects that one or more axes failed to complete the reference point return sequence properly. This is typically caused by incorrect reference point parameters, position coder/encoder issues, dog switch problems, or mechanical interference preventing the axis from reaching the grid reference position.

Safety

Machine not referenced

Causes and Fixes

1
Navigate to SYSTEM > PARAM and verify parameter 1815 for each axis. Bit 0 controls reference point return direction (0=negative, 1=positive). Bit 1 sets dog-type (0=one-side, 1=both-side proximity switch).
2
Check parameter 1240 (grid shift amount). This must match the encoder's grid pitch. For absolute encoders, verify battery voltage is above 3.0V in DIAGNOSIS screen (battery voltage diagnostic #1000 series depending on control model).
3
If using incremental encoders, verify parameter 1815 bit 5 (grid-type reference point) is set correctly. Execute reference point return again after confirming all parameters match the machine mechanical configuration.
4
For absolute encoders with lost reference, execute the reference point establishment procedure per Fanuc maintenance manual using G28 with proper PMC dog signals, then perform battery replacement if voltage is low.
Changing parameter 1815 incorrectly can cause axis collision. Record original values before modification.

DIY Feasiblehigh confidence

Call a technician if:

·Encoder replacement required
·Servo amplifier communication errors persist
·Mechanical reference position unknown

Prevention

Replace encoder batteries every 2-3 years
Perform reference return at consistent positions
Keep encoder assemblies clean and protected
Monitor servo load trends during reference return

Common Mistakes

Setting reference return speed too high
Ignoring encoder battery warnings
Attempting reference return from random positions
Not verifying mechanical reference position before absolute reset

Related Alarms

091 092 300 301 310

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