This page covers FANUC SV alarms related to synchronization control, APC communication, built-in pulse coders, and external detectors. These alarms are commonly associated with position feedback, absolute position detection, encoder communication, detector data errors, and synchronization performance between axes. For maintenance engineers and machine tool service teams, this group of SV alarms is important because it often points to feedback problems, detector cable issues, APC communication faults, or synchronization deviations that affect machine motion accuracy.
These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D.
At REACO CNC, we supply FANUC CNC parts, FANUC robot parts, Mitsubishi automation parts, and repair services for customers worldwide. If your machine is showing FANUC servo alarms related to feedback, APC, or encoder signals, this page can help you identify the alarm meaning before moving on to inspection, repair, or replacement decisions.
What These FANUC SV Alarms Usually Indicate
This section of the FANUC SV alarm list mainly relates to synchronization control, APC communication, internal pulse coders, and external position detectors. In practical maintenance work, these alarms are often connected to detector communication errors, abnormal feedback data, encoder signal loss, detector wiring defects, or synchronization conditions that exceed configured limits. Some alarms occur on the master axis, some on the slave axis, and others are generated when the CNC cannot correctly obtain mechanical position data from the detector system.
Common Causes of FANUC Synchronization, APC and Encoder Alarms
In many cases, these alarms appear because of communication faults between the CNC and the detector system, feedback signal abnormalities, cable problems, detector defects, incorrect parameter settings, or synchronization deviations that exceed the allowed values. On machines using absolute position detection, APC-related alarms may also appear when the control fails to calculate the mechanical position correctly due to transmission errors, timeout conditions, pulse errors, overflow conditions, or detector-related hardware faults.
For built-in pulse coders and external detectors, common field causes include damaged cables, poor connector contact, detector failure, abnormal phase data, communication errors, CRC errors, lost pulses, lost count values, or interface module faults. In synchronization control, alarms may also be triggered when compensation values, synchronization errors, mechanical coordinate differences, or torque-related conditions exceed the parameter limits defined in the CNC.
Full FANUC SV Alarm List: Synchronization, APC and Encoder Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0001 | Synchronization calibration error | In feed axis synchronization control, the compensation amount during synchronization adjustment exceeded the value set in parameter (No.8325). This alarm occurs on either the master axis or the slave axis. |
| SV0002 | Excessive synchronization error alarm 2 | In feed axis synchronization control, the synchronization error exceeded the value set in parameter (No.8332). After power-on, before synchronization adjustment has been completed, the judgment is made using the value of parameter (No.8332) multiplied by the multiplier set in parameter (No.8330). This alarm occurs only on the slave axis. |
| SV0003 | Synchronization / composite / overlap control mode cannot continue [T] | A servo alarm occurred on an axis operating in synchronization, composite, or overlap control mode, and that control mode can no longer continue. When a servo alarm is issued on any axis in that control group, all related axes are placed in servo-off status. This alarm is issued so that the reason for the servo-off condition can be identified. |
| SV0004 | G31 excessive error | During torque-limit skip command operation, the position deviation exceeded the limit set in parameter (No.6287). |
| SV0005 | Excessive synchronization error (mechanical coordinate) | During synchronized feed axis operation, the difference in mechanical coordinates between the master axis and the slave axis exceeded the value set in parameter (No.8314). This alarm occurs on either the master axis or the slave axis. |
| SV0006 | Dual motor drive axis incorrect | In the slave axis of tandem control, absolute position detection has been set incorrectly by enabling APC (No.1815#5)=1. |
| SV0007 | Servo warning on another path (multi-axis amplifier) [T] | In a 2-path system where a multi-axis amplifier is used across paths, a servo alarm occurred on an axis belonging to another path. When multiple servo axes across paths are controlled by a single multi-axis amplifier, a servo alarm on an axis in another path may cause the amplifier MCC to drop, which in turn generates SV0401 “Servo V-ready signal off” on an axis in the current path using the same amplifier. SV0401 in this case is caused by a servo alarm on an axis in another path. Investigate the cause of the servo alarm on the axis in the other path that shares the same amplifier. |
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0301 | APC alarm: communication error | Due to a communication error in the absolute position detector, the mechanical position could not be obtained correctly. (Data transmission abnormality.) The absolute position detector, cable, or servo interface module may be defective. |
| SV0302 | APC alarm: timeout error | Due to a timeout error in the absolute position detector, the mechanical position could not be obtained correctly. (Data transmission abnormality.) The absolute position detector, cable, or servo interface module may be defective. |
| SV0303 | APC alarm: data format error | Due to a frame error in the absolute position detector, the mechanical position could not be obtained correctly. (Data transmission abnormality.) The absolute position detector, cable, or servo interface module may be defective. |
| SV0304 | APC alarm: parity error | Due to a parity error in the absolute position detector, the mechanical position could not be obtained correctly. (Data transmission abnormality.) The absolute position detector, cable, or servo interface module may be defective. |
| SV0305 | APC alarm: pulse error | Due to a pulse error in the absolute position detector, the mechanical position could not be obtained correctly. The absolute position detector or cable may be defective. |
| SV0306 | APC alarm: overflow alarm | Position deviation overflow occurred and the mechanical position could not be obtained correctly. Check parameters (No.2084, No.2085). |
| SV0307 | APC alarm: axis movement too large | Due to excessive machine movement at power-on, the mechanical position could not be obtained correctly. |
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0360 | Pulse coder code check sum error (built-in) | A checksum alarm occurred in the built-in pulse coder. |
| SV0361 | Pulse coder phase abnormality (built-in) | A phase data abnormality alarm occurred in the built-in pulse coder. |
| SV0362 | REV. data abnormality (INT) | A rotation count abnormality alarm occurred in the built-in pulse coder. |
| SV0363 | Clock abnormality (built-in) | A clock alarm occurred in the built-in pulse coder. |
| SV0364 | Soft response alarm (built-in) | The digital servo software detected an abnormality in the built-in pulse coder. |
| SV0365 | LED abnormality (built-in) | LED abnormality in the built-in pulse coder. |
| SV0366 | Pulse loss (built-in) | Pulse loss occurred in the built-in pulse coder. |
| SV0367 | Count value loss (built-in) | Count value loss occurred in the built-in pulse coder. |
| SV0368 | Serial data error (built-in) | Communication data from the built-in pulse coder could not be received. |
| SV0369 | Data transfer error (built-in) |
During reception of communication data from the built-in pulse coder, a CRC error or stop-bit error occurred. |
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0380 | LED abnormality (external) | Error in the external detector. |
| SV0381 | Encoder phase abnormality (external) | A position data abnormality alarm occurred in the external linear scale. |
| SV0382 | Count value loss (external) | Count value loss occurred in the external detector. |
| SV0383 | Pulse loss (external) | Pulse loss occurred in the external detector. |
| SV0384 | Soft response alarm (external) | The digital servo software detected abnormal data from the external detector. |
| SV0385 | Serial data error (external) | Communication data from the external detector could not be received. |
| SV0386 | Data transfer error (external) | During reception of communication data from the external detector, a CRC error or stop-bit error occurred. |
| SV0387 | Encoder abnormality (external) | Some kind of abnormality occurred in the external detector. For details, contact the manufacturer of the linear scale. |
Practical Inspection Notes for APC and Encoder Related SV Alarms
When APC or encoder-related SV alarms appear, the first step is usually to confirm whether the detector system is stable and correctly connected. In practice, service engineers often inspect detector cables, connector seating, signal transmission quality, interface modules, and recent maintenance history before replacing major components. A communication error does not always mean the detector itself is damaged; in many cases, the cause may be poor cable contact, signal corruption, unstable power conditions, or a problem in the related servo interface path.
For built-in pulse coder alarms, attention should be given to checksum errors, phase abnormalities, pulse loss, and communication failures. For external detector alarms, the inspection may also involve the linear scale, external detector cable, and detector interface hardware. If a synchronization-related alarm is generated, it is also important to compare the machine condition with the relevant parameter settings and confirm whether the deviation exceeded the configured limit during operation.
REACO CNC Support for FANUC Servo and Feedback Related Issues
REACO CNC supplies FANUC CNC spare parts, FANUC robot parts, Mitsubishi automation parts, and repair services for industrial customers worldwide. If your machine is showing APC, encoder, detector, or synchronization-related SV alarms, our team can help support your spare parts sourcing and repair needs for related FANUC components.
With 34 years of experience, REACO CNC serves customers around the world with global shipping, technical product support, and repair solutions for industrial automation equipment.
FAQ
What does a FANUC APC alarm usually mean?
In general, it means the CNC could not correctly obtain mechanical position data from the absolute position detector. This may be related to communication errors, timeout conditions, pulse errors, overflow conditions, or detector-related faults.
Are APC alarms always caused by a bad encoder?
Not always. The detector itself may be faulty, but the cause can also be the cable, the servo interface module, signal transmission errors, or unstable detector communication.
What is the difference between built-in pulse coder alarms and external detector alarms?
Built-in pulse coder alarms are related to the detector integrated with the motor or internal feedback system, while external detector alarms are related to an external feedback device such as a linear scale or other external detector hardware.
Why does a synchronization alarm appear on the slave axis?
Some synchronization alarms are defined to occur specifically on the slave axis when the synchronization error exceeds the allowed parameter value during feed axis synchronization control.
Which machines does this alarm reference apply to?
These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D.
Reference Source: Beijing FANUC. This article is based on technical documentation provided by Beijing FANUC.
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