What causes FANUC alarm 305?

G29 programmed without a preceding G28 or G30 in the same tool change sequence. G29 in a subprogram called without the required G28/G30 being executed first. Program restarted mid-cycle at a block containing G29 without the reference return history. Intermediate position cleared by a mode change or reset before G29 executed.

How do I fix FANUC alarm 305?

1. Always program G28 or G30 before G29 in the same sequence. 2. Do not use G29 without a preceding reference return command in the current cycle. 3. If restarting mid-program, restart from a point before the G28/G30 that precedes G29. 4. Review the Fanuc programming manual for the correct G28-G29 tool change sequence.

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FANUC Controller

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

Alarm 305

Fanuc Alarm 305 - INTERMEDIATE POSITION IS NOT ASSIGNED

Fanuc 305 APC ALARM indicates the absolute pulse coder (encoder) on the specified axis has detected a pulse count mismatch or signal loss during position verification. This typically occurs due to mechanical coupling failure between motor and encoder, encoder hardware failure, or cable/connector issues disrupting the serial communication between the absolute encoder and the servo amplifier.

FANUCProgram/G-codeIntermediate30-90 minutes

305

Fanuc Alarm 305 - INTERMEDIATE POSITION IS NOT ASSIGNED

INTERMEDIATE POSITION IS NOT ASSIGNED

Root Cause Summary

Fanuc 305 APC ALARM indicates the absolute pulse coder (encoder) on the specified axis has detected a pulse count mismatch or signal loss during position verification. This typically occurs due to mechanical coupling failure between motor and encoder, encoder hardware failure, or cable/connector issues disrupting the serial communication between the absolute encoder and the servo amplifier.

Causes and Fixes

1
Power off the machine and manually rotate the affected axis motor shaft while observing for mechanical resistance, binding, or loose coupling between motor and encoder. Check encoder mounting bolts for proper torque.
Ensure all power is removed and verify using EMERGENCY STOP before manual manipulation
2
Access DIAGNOSIS screen path: SYSTEM > DIAGNOSIS > #300-#307 (Servo load meter) for the affected axis. Review historical load data to identify sudden spikes that may indicate mechanical shock to the encoder.
3
Check diagnostic #400-#407 (Absolute position data) and #408-#415 (Absolute position pulse count). Compare values before and after manual rotation to verify encoder is counting correctly. Inconsistent counts confirm encoder failure.
4
If coupling is intact but alarm persists, replace the absolute pulse coder assembly. After replacement, execute absolute encoder reference position setup per Fanuc Servo Manual: SYSTEM > PMC > SETTING > Initialize absolute position (#1815.0=1).
Replacing encoder requires re-establishing absolute reference position using reference position setup procedure

DIY Feasiblehigh confidence

Call a technician if:

·Encoder replacement required
·Servo amplifier replacement needed
·Multiple axes affected simultaneously

Prevention

Regular encoder cable inspection during PM
Maintain proper cable routing in carriers
Monitor encoder power supply voltage monthly
Keep encoder assemblies clean and dry

Common Mistakes

Ignoring loose coupling set screws during PM
Using wrong encoder part number during replacement
Grounding encoder shield at both ends
Not recording encoder position before removal

Related Alarms

300 301 304 308 401

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