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FANUC Alarm Code Guide

Find solutions to common Fanuc CNC alarm codes quickly and efficiently.

Servo Alarm
Spindle Alarm
System Alarm
Overtravel Alarm

FANUC Alarms: Quick Guide to Get Back Online​

When your FANUC CNC triggers an alarm, it's trying to tell you something. From simple overtravel to complex servo issues, these codes pinpoint where the problem lies.Our guide cuts through the complexity. We explain the most common alarms—what they mean, why they happen, and how to fix them. Whether you're facing alarm 401 or a stuck overtravel limit, you'll find clear, step-by-step solutions to minimize downtime.​​ You will learn how to:​​

  • Decode any FANUC alarm number.
  • Diagnose faults in servos, spindles, or system memory.
  • Perform basic checks before calling a technician.
  • Identify components that may need adjustment or replacement.

Get the knowledge to solve problems faster and keep your machines running.
FANUC SV0435 Alarm: Inverter DC Link Low Voltage
The FANUC SV0435 alarm indicates an inverter DC link low voltage condition. This alarm occurs when the DC link voltage, also called the DC bus voltage, inside the servo amplifier drops below the required level. In a FANUC servo system, the servo amplifier depends on a stable DC bus voltage for normal inverter operation. If the DC link connection is loose, the wiring is incorrect, the DC bus connection cable or bus bar is not properly tightened, the amplifier control circuit board is not inserted correctly, or the servo drive... Read more...
FANUC SV0434 Alarm: Inverter Control Voltage Low
The FANUC SV0434 alarm indicates an inverter control voltage low condition. This alarm occurs when the control power voltage of the servo amplifier drops below the required level. The servo amplifier requires a stable control power supply for normal operation. If the control voltage becomes too low, the CNC system may detect an abnormal amplifier control power condition and generate the SV0434 alarm. This alarm may be related to abnormal DC24V output from the common power supply, incorrect jumper cable connection between servo amplifiers, feedback cable problems, external control circuits... Read more...
FANUC SV0433 Alarm: Inverter DC Link Voltage Low
The FANUC SV0433 alarm indicates an inverter DC link voltage low condition. This alarm occurs when the DC voltage in the main circuit, also known as the DC bus voltage or DC link voltage, drops below the required level. In FANUC servo systems, the servo amplifier or common power supply module depends on stable main circuit input power. If the main power voltage drops, the DC link wiring is loose, the magnetic contactor does not operate correctly, or the emergency stop circuit prevents the main power from being supplied, the... Read more...
FANUC SV0432 Alarm: Inverter Control Voltage Low
The FANUC SV0432 alarm indicates an inverter control voltage low condition. This alarm occurs when the control voltage of the servo amplifier or common power supply drops below the required level. In many cases, SV0432 is related to a voltage drop in the servo amplifier system, the common power supply input module, or the internal control power supply circuit. It may also be caused by poor connection between servo amplifiers, insufficient input voltage, abnormal 24V control power, insufficient power supply capacity, external wiring problems, or a faulty common power supply... Read more...
FANUC SV431 Alarm: Inverter Circuit Normal
The FANUC SV431 alarm is related to the inverter circuit normal signal. This alarm may occur when the CNC system detects an abnormal condition related to the servo amplifier, common power supply, or related alarm signal circuit. In many cases, SV431 is associated with servo amplifier overheating or common power supply overheating. It may also be related to incorrect amplifier wiring, incorrect ALM signal handling, analog servo adapter wiring issues, incorrect motor parameters, or servo amplifier failure. Because this alarm can involve both signal wiring and actual servo hardware condition,... Read more...
FANUC SV0430 Alarm: Servo Motor Overheat
FANUC SV0430 Alarm: Servo Motor Overheat
The FANUC SV0430 alarm indicates a servo motor overheat condition. This alarm occurs when the temperature detection element inside the encoder detects that the servo motor temperature is too high.... Read more...
FANUC SV0423 Alarm: Excessive Error in Torque Control
The FANUC SV0423 alarm indicates an excessive error in torque control. This alarm occurs when the accumulated movement value in torque control exceeds the allowable value set by parameter. In torque control mode, the CNC system monitors not only the torque command but also the movement accumulation allowed during torque control. If the accumulated movement becomes larger than the permitted threshold, the system may generate the SV0423 alarm. This alarm is usually related to the torque control movement accumulation parameter, torque control program logic, actual mechanical condition, or an unsuitable... Read more...
FANUC SV0422 Alarm: Torque Control Overspeed
The FANUC SV0422 alarm indicates a torque control overspeed condition. This alarm occurs when the allowable speed specified in torque control has been exceeded. In torque control mode, the CNC system controls the servo axis according to a torque command while also monitoring the allowed speed limit. If the actual or commanded operating condition exceeds the specified allowable speed in torque control, the system may generate the SV0422 alarm. This alarm is mainly related to the torque control command, torque setting value, speed limit value, torque control parameters, and the... Read more...
FANUC SV0421 Alarm: Excess Error in Semi-Closed Loop Control
The FANUC SV0421 alarm indicates an excess error in semi-closed loop control. This alarm occurs when the difference between the full-closed loop feedback data and the semi-closed loop calculated data exceeds the value set in parameter P2118. In a servo system using both semi-closed loop and full-closed loop feedback, the CNC system compares the motor-side calculated position with the machine-side feedback position. If the difference between these two values becomes larger than the allowable range, the system may generate the SV0421 alarm. This alarm is usually related to incorrect parameter... Read more...
FANUC SV0420 Alarm: Excessive Synchronous Torque Difference
The FANUC SV0420 alarm indicates an excessive synchronous torque difference. This alarm occurs during synchronous operation in feed axis synchronous control when the torque difference between the master axis and the slave axis exceeds the value set in the CNC system. In a feed axis synchronous control system, the master axis and slave axis must operate together with a balanced torque relationship. If the torque difference becomes too large, the CNC system may generate the SV0420 alarm to protect the mechanical structure and servo system. This alarm occurs on the... Read more...
FANUC SV0417 Alarm: Illegal Digital Servo Parameter
The FANUC SV0417 alarm indicates an illegal digital servo parameter. This alarm occurs when an abnormal or invalid parameter setting is detected in the digital servo system. Digital servo parameters are essential for matching the CNC control system with the servo motor, feedback system, rotation direction, and axis control configuration. If one or more digital servo parameters are set incorrectly, the CNC system may detect the abnormal setting and generate the SV0417 alarm. For this alarm, the first important diagnostic point is diagnosis N203#4. The troubleshooting direction depends on whether... Read more...
FANUC SV0415 Alarm: Excessive Movement
The FANUC SV0415 alarm indicates an excessive movement condition. This alarm occurs when a command speed higher than the allowed movement speed limit is specified. In normal CNC operation, the commanded movement speed must remain within the allowable range of the servo control system and machine configuration. If the specified command speed exceeds the movement speed limit, the CNC system may generate the SV0415 alarm to prevent abnormal servo operation. This alarm is mainly related to excessive command speed. In some special applications, such as gear machining using FSC +... Read more...

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