This page covers FANUC SV alarms related to servo amplifiers, drive circuits, current detection, voltage status, DC link conditions, cooling fan faults, detector disconnection, FSSB communication, and servo hardware configuration. These alarms are especially important in maintenance and repair work because they are often associated with amplifier health, power conditions, wiring integrity, cooling performance, and system-level servo communication.
These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D.
For service engineers, maintenance teams, and machine owners, this group of SV alarms is one of the most practical parts of the FANUC alarm list because it often points to real hardware issues, unstable power conditions, cable faults, amplifier abnormalities, or incorrect configuration between motors, amplifiers, and control software. At REACO CNC, we supply FANUC CNC parts, FANUC robot parts, Mitsubishi automation parts, and repair services for customers worldwide.
What These FANUC SV Alarms Usually Indicate
This section of the FANUC SV alarm list mainly relates to servo amplifier operation, power and voltage conditions, current abnormalities, detector line problems, control readiness signals, parameter mismatches, FSSB communication, and amplifier or motor configuration issues. In practical field service, these alarms often appear when the control detects unstable drive conditions, abnormal detector feedback, servo software mismatch, cooling failure, excessive load, disconnection, or hardware trouble in the amplifier system.
Some of these alarms are caused by internal amplifier faults, while others are triggered by external factors such as damaged cables, incorrect parameter settings, poor cooling, grounding problems, power supply instability, or communication failure between the CNC and the servo amplifier system. Because many of these alarms directly affect axis motion and servo readiness, accurate diagnosis is important before replacing parts.
Common Causes of Servo Amplifier and Drive Related SV Alarms
In real maintenance work, common causes of these alarms include amplifier overheating, abnormal motor current, DC link overvoltage or undervoltage, power supply problems, detector cable disconnection, poor board connection, fan failure, incorrect motor-amplifier pairing, FSSB communication interruption, or an incorrect combination of axis card and servo software.
Some alarms may also be linked to excessive machine load, grounding faults, unstable incoming power, regenerative discharge problems, HRV setting mismatch, or a detector-related signal inconsistency between built-in and external feedback devices. When these alarms repeat, it is usually important to check not only the alarm code itself but also the wider machine condition, including wiring, cooling, connector contact, recent maintenance history, and parameter settings.
Full FANUC SV Alarm List: Servo Amplifier, Drive, Voltage and Overheat Alarms
Table 1. Servo Amplifier, CPU, Current and Power Supply Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0010 | SV OVERHEAT | Internal overheating occurred in the amplifier. |
| SV0011 | SV MOTOR OVER CURRENT (SOFT) | The digital servo software detected an abnormal command value. Possible causes include an unconnected power cable, cable breakage (phase loss), or short circuit. |
| SV0012 | SV DRIVE OFF CIRCUIT FAILURE | The states of the two shut-off inputs do not match, or the shut-off circuit is abnormal. |
| SV0013 | SV CPU bus error | Abnormal data occurred on the internal CPU bus of the amplifier. |
| SV0014 | SV CPU watchdog | An abnormality occurred in the CPU operation inside the amplifier. |
| SV0015 | SV LOW VOLT DRIVER | The internal drive power supply voltage in the amplifier dropped. Possible causes include poor insertion of the control board or an amplifier fault. |
| SV0016 | SV CURRENT DETECT ERROR | Abnormality occurred in the motor current detection data inside the amplifier. Possible causes include poor insertion of the control board or an amplifier fault. |
| SV0017 | SV INTERNAL SERIAL BUS FAILURE | Abnormality occurred in the internal serial bus communication inside the amplifier. Possible causes include poor insertion of the control board or an amplifier fault. |
| SV0018 | SV ROM DATA FAILURE | Abnormality occurred in the ROM data inside the amplifier. |
| SV0019 | SV MOTOR OVER CURRENT (GND FAULT) | Ground fault in the motor, power cable, or amplifier. |
| SV0020 | PS GROUND FAULT | Ground fault in the motor, power cable, or amplifier. |
| SV0021 | PS OVERCURRENT 2 | Overcurrent flowed into the input circuit section. |
| SV0022 | PS OVERCURRENT 3 | Overcurrent flowed into the input circuit section. |
| SV0023 | PS OVERCURRENT 4 | Overcurrent flowed into the input circuit section. |
| SV0024 | PS SOFT THERMAL | A load exceeding the rated value was applied. |
| SV0025 | PS DC LINK overvoltage 2 | DC LINK voltage is too high. |
| SV0026 | PS DC LINK overvoltage 3 | DC LINK voltage is too high. |
| SV0027 | PS DC LINK overvoltage 4 | DC LINK voltage is too high. |
| SV0028 | PS DC LINK low voltage 2 | DC LINK voltage dropped. |
| SV0029 | PS DC LINK low voltage 3 | DC LINK voltage dropped. |
| SV0030 | PS DC LINK low voltage 4 | DC LINK voltage dropped. |
| SV0031 | PS ILLEGAL PARAMETER | An illegal value has been set in the PS control parameters. |
| SV0034 | PS HARDWARE ERROR | PS hardware abnormality. |
| SV0040 | PS SUB MODULE ERROR 1 | Defect in the PS auxiliary module, PS unit, or cable. Replacement is required. |
| SV0041 | PS SUB MODULE ERROR 2 | Defect in the PS auxiliary module, PS unit, or cable. Replacement is required. |
| SV0042 | PS SUB MODULE ERROR 3 | Defect in the PS auxiliary module, PS unit, or cable. Replacement is required. |
| SV0043 | PS SUB MODULE ERROR 4 | Defect in the PS auxiliary module, PS unit, or cable. Replacement is required. |
Table 2. Servo Ready, Parameter, Deviation and Detector Line Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0401 | Servo V-ready signal off | The position control ready signal (PRDY) is on, but the speed control ready signal (VRDY) is off. |
| SV0403 | Hardware / software mismatch | The combination of the axis card and servo software is incorrect. Possible causes include: 1) the correct axis card has not been installed; 2) the correct servo software has not been installed in flash memory. |
| SV0404 | Servo V-ready signal on | The position control ready signal (PRDY) is off, but the speed control ready signal (VRDY) is on. |
| SV0407 | Excessive error [T] | The position deviation of the synchronized axis exceeded the set value. (Synchronization control only.) |
| SV0409 | Detected torque abnormal | An abnormal load was detected in the servo motor, Cs axis, or spindle positioning axis (T series). This alarm cannot be cleared by RESET. |
| SV0410 | Excessive error at stop | The position deviation at stop exceeded the value set in parameter (No.1829). |
| SV0411 | Excessive error during motion | The position deviation during movement was much larger than the value set in parameter (No.1828). |
| SV0413 | Axis LSI overflow | The counter for position deviation overflowed. |
| SV0415 | Excessive travel amount | A speed exceeding the movement speed limit was specified. |
| SV0417 | Illegal digital servo parameter | The digital servo parameter settings are incorrect. When diagnostic information No.203#4=1, the servo software detected an illegal parameter. Use diagnostic information No.352 to determine the cause. When diagnostic information No.203#4=0, the CNC software detected an illegal parameter. Possible causes include: 1) a motor model value outside the specified range has been set in parameter (No.2020); 2) the motor rotation direction in parameter (No.2022) has not been set correctly (111 or -111); 3) parameter (No.2023) for the velocity feedback pulses per motor revolution has been set to an invalid value below 0; 4) parameter (No.2024) for the position feedback pulses per motor revolution has been set to an invalid value below 0. |
| SV0420 | Excessive synchronization torque difference | During synchronized operation in feed axis synchronization control, the torque difference between the master axis and the slave axis exceeded the value set in parameter (No.2031). This alarm occurs only on the master axis. |
| SV0421 | Excessive deviation (semi-closed loop) | The feedback difference between the SEMI side and the FULL side exceeded the value set in parameter (No.2118). |
| SV0422 | Overspeed in torque control | The allowable speed specified in torque control was exceeded. |
| SV0423 | Excessive error in torque control | In torque control, the allowable accumulated movement value set by parameter was exceeded. |
| SV0445 | Soft disconnection alarm | The digital servo software detected a pulse coder disconnection. |
| SV0446 | Hard disconnection alarm | The built-in pulse coder disconnection was detected by hardware. |
| SV0447 | Hard disconnection alarm (external) | The external detector disconnection was detected by hardware. |
| SV0448 | Feedback inconsistency alarm | The sign of the data fed back from the built-in pulse coder is opposite to the sign of the data fed back from the external detector. |
| SV0453 | Serial encoder disconnection alarm | Software disconnection alarm for the α pulse coder. With CNC power turned off, temporarily unplug the pulse coder cable. If the alarm occurs again, replace the pulse coder. |
| SV0454 | Illegal rotor position detection | Pole detection function ended abnormally. The motor did not move and magnetic pole position detection could not be performed. |
| SV0456 | Illegal current loop | The configured current control cycle cannot be set. The amplifier pulse module used is not suitable for high-speed HRV, or the system does not satisfy the conditions required for high-speed HRV control. |
| SV0458 | Current loop error | The configured current control cycle differs from the actual current control cycle. |
| SV0459 | High-speed HRV setting error | In the two adjacent axes specified by servo axis number (parameter No.1023), one of the odd/even axis pair can perform high-speed HRV control, while the other cannot. |
| SV0466 | Motor / amplifier combination incorrect | The maximum current value of the amplifier and the maximum current value of the motor do not match. Possible causes include: 1) incorrect assignment of axis and amplifier connection; 2) incorrect setting of parameter (No.2165). |
| SV0468 | High-speed HRV setting error (AMP) | High-speed HRV has been set for an axis controlled by an amplifier that does not support high-speed HRV. |
Table 3. Overheat, Voltage, Fan, IPM and Regeneration Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0430 | Servo motor overheat | The servo motor has overheated. |
| SV0431 | Inverter circuit overload | Common power supply: overheating. Servo amplifier: overheating. |
| SV0432 | Inverter control voltage low | Common power supply: control power voltage dropped. Servo amplifier: control power voltage dropped. |
| SV0433 | Inverter DC LINK voltage low | Common power supply: DC LINK voltage dropped. Servo amplifier: DC LINK voltage dropped. |
| SV0434 | Inverter control voltage low | Servo amplifier: control power voltage dropped. |
| SV0435 | Inverter DC LINK low voltage | Servo amplifier: DC LINK voltage dropped. |
| SV0436 | Soft thermal relay (OVC) | The digital servo software detected soft thermal protection (OVC). |
| SV0437 | Inverter input circuit overcurrent | Common power supply: overcurrent flowed into the input circuit. |
| SV0438 | Inverter current abnormal | Servo amplifier: motor current is too large. |
| SV0439 | Inverter DC LINK overvoltage | Common power supply: DC LINK voltage is too high. Servo amplifier: DC LINK voltage is too high. |
| SV0440 | Inverter deceleration power too large | Common power supply: regenerative discharge amount is too large. Servo amplifier: regenerative discharge amount is too large, or the regenerative discharge circuit is abnormal. |
| SV0441 | Abnormal current offset | The digital servo software detected an abnormality in the motor current detection circuit. |
| SV0442 | DC LINK charge abnormality in inverter | Common power supply: abnormality in the backup discharge circuit of the DC LINK. |
| SV0443 | Inverter cooling fan failure | Common power supply: internal stirring fan failure. Servo amplifier: internal stirring fan failure. |
| SV0444 | Inverter cooling fan failure | Servo amplifier: internal stirring fan failure. |
| SV0449 | Inverter IPM alarm | Servo amplifier: IPM (intelligent power module) detected an alarm. |
| SV0600 | Inverter DC LINK overcurrent | DC LINK current is too large. |
| SV0601 | Inverter heat sink fan failure | Failure of the fan for cooling the external heat sink. |
| SV0602 | Inverter overheat | Servo amplifier overheated. |
| SV0603 | Inverter IPM alarm (overheat) | IPM (intelligent power module) detected an overheat alarm. |
| SV0605 | Inverter regenerative discharge power too large | Common power supply: motor regenerative power is too large. |
| SV0606 | Inverter cooling fan stopped | Common power supply: failure of the fan for cooling the external heat sink. |
| SV0607 | Inverter main power phase loss | Common power supply: input power phase loss. |
| SV0654 | DB relay abnormality | Abnormality in the dynamic braking relay of the servo amplifier. Replace the amplifier. |
Table 4. FSSB Communication, Initialization and Configuration Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0460 | FSSB disconnection | FSSB communication was suddenly disconnected. Possible causes include: 1) FSSB communication cable disconnected or broken; 2) amplifier power suddenly shut off; 3) amplifier issued a low-voltage alarm. |
| SV0462 | CNC data transfer error | Due to an FSSB communication error, correct data cannot be received on the driven side. |
| SV0463 | Slave data transmission failed | Due to an FSSB communication error, the servo software cannot receive correct data. |
| SV0465 | ID data read failed | At power-on, the initial ID information of the amplifier could not be read. |
| SV0604 | Amplifier communication error | Communication abnormality between the servo amplifier and the common power supply. |
| SV1025 | V-ready signal abnormal (initialization) | When servo control is turned on, the speed control ready signal (VRDY) should be off, but it is already on. |
| SV1026 | Illegal axis assignment | The servo axis arrangement parameters have not been set correctly. In parameter (No.1023) “servo axis number for each axis,” a negative value, duplicate value, or value larger than the number of controlled axes has been set. |
| SV1055 | Dual motor drive axis incorrect | In tandem control, the setting of parameter (No.1023) is incorrect. |
| SV1056 | Dual motor drive axis pair setting incorrect | In tandem control, the setting of TDM (No.1817#6) is incorrect. |
| SV1067 | FSSB: configuration error (software) | An FSSB configuration error (software detection) occurred. The connected amplifier type differs from the FSSB setting value. |
| SV1100 | Straightness compensation overflow [M] | Straightness compensation value exceeded the maximum value 32767. |
| SV5134 | FSSB: power-on timeout | During initialization, FSSB did not enter the ready-open state. The axis card may be defective. |
| SV5136 | FSSB: insufficient amplifiers | Compared with the number of controlled axes, the number of amplifiers recognized by FSSB is insufficient. The axis count setting or amplifier connection is incorrect. |
| SV5137 | FSSB: configuration error | An FSSB configuration error occurred. The connected amplifier type differs from the FSSB setting value. |
| SV5139 | FSSB: error | Servo initialization did not end normally. Possible causes include defective optical cable or incorrect connection between the amplifier and other modules. |
| SV5197 | FSSB: power-on timeout | Although the CNC permitted FSSB to open, FSSB did not open. Check the connection status between the CNC and the amplifier. |
Table 5. External Detector Analog Signal Alarm
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| SV0646 | Analog signal abnormality (external) | The analog 1Vp-p output of the external detector is abnormal. Possible causes include failure of the external detector, cable, or external detector interface unit. |
Practical Inspection Notes
When amplifier-related SV alarms appear, the first checks usually include the machine’s incoming power condition, amplifier status, connector seating, cable integrity, cooling airflow, and whether any overload or regeneration condition has been occurring during operation. Alarms related to overcurrent, overvoltage, low voltage, or DC LINK conditions should be reviewed together with the actual running condition of the machine, because repeated load spikes, unstable power, braking demand, or poor cooling may all contribute to recurrence.
For detector disconnection and feedback inconsistency alarms, inspection should usually include pulse coder cables, external detector cables, connector contact, detector mounting condition, and whether the machine has both built-in and external feedback systems configured correctly. For FSSB alarms, it is often necessary to inspect the optical communication path, amplifier power state, axis assignment, amplifier type matching, and initialization sequence. In many cases, replacing a part too early can waste time if the real cause is wiring, power instability, or configuration mismatch.
REACO CNC Support
REACO CNC supplies FANUC CNC parts, FANUC robot parts, Mitsubishi automation parts, and repair services for customers worldwide. If your machine shows FANUC servo amplifier, FSSB, power supply, or feedback-related alarms, we can support your spare parts sourcing and repair requirements for industrial automation systems.
With 34 years of experience, REACO CNC supports global customers with worldwide shipping, tested industrial parts, and repair solutions for FANUC and Mitsubishi equipment.
FAQ
Is a FANUC SV amplifier alarm always caused by a bad amplifier?
Not always. Some amplifier-related alarms are caused by the amplifier itself, but others may be linked to cable faults, power instability, grounding problems, overload conditions, cooling issues, or parameter mismatch.
What does a DC LINK alarm usually mean on FANUC systems?
It generally means the control detected an abnormal DC LINK condition, such as overvoltage, undervoltage, overcurrent, or charging abnormality in the servo power system.
What should be checked when an FSSB alarm appears?
Typical checks include the FSSB cable condition, amplifier power status, optical connection integrity, initialization state, axis assignment, and whether the connected amplifier type matches the configured setting.
What does SV0445 or SV0453 suggest?
These alarms point to pulse coder or serial encoder disconnection conditions detected by software or related monitoring logic. Cable condition and encoder connection should be checked carefully.
Which machines does this 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.
For More Fanuc CNC repair Cases and technical articles, please back to Fanuc Technical Support Center.
Related Pages
- FANUC SV Alarm Codes: Synchronization, APC and Encoder Alarms
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