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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 SV0447 Alarm: Hard Disconnection External Detector
The FANUC SV0447 alarm indicates a hard disconnection alarm for the external detector. This alarm occurs when hardware detects a disconnection in the external detector feedback circuit. SV0447 usually occurs in a full-closed loop system, where the CNC system uses an external detector such as a linear scale, external encoder, or rotary encoder to detect the actual machine position. If the external detector signal is interrupted, the feedback cable is disconnected, the connector is loose, or the detector itself is faulty, the CNC system may generate the SV0447 alarm. Unlike... Read more...
FANUC SV0446 Alarm: Hard Disconnection Alarm
The FANUC SV0446 alarm indicates a hard disconnection alarm. This alarm occurs when hardware detects a disconnection in the built-in pulse encoder. The built-in pulse encoder is used to send motor feedback signals to the servo system. If the encoder feedback signal is interrupted, the encoder connector is loose, the motor feedback cable is damaged, or the encoder itself is faulty, the CNC system may generate the SV0446 alarm. Unlike SV0445, which is detected by digital servo software as a soft disconnection alarm, SV0446 is detected by hardware. Therefore, troubleshooting... Read more...
FANUC SV0445 Alarm: Soft Disconnection Alarm
The FANUC SV0445 alarm indicates a soft disconnection alarm. This alarm occurs when the digital servo software detects a disconnection in the pulse encoder signal. SV0445 is commonly seen in full-closed loop systems using an external detector, such as a linear scale, external pulse encoder, or rotary encoder. It belongs to an external detector pulse encoder alarm. When the CNC system detects an abnormal feedback signal or possible encoder disconnection, the SV0445 alarm may appear. This alarm may be caused by incorrect parameter settings, feedback cable disconnection, poor connector contact,... Read more...
FANUC SV0444 Alarm: Inverter Cooling Fan Failure
The FANUC SV0444 alarm indicates an inverter cooling fan failure. This alarm occurs when the servo amplifier detects that the internal cooling fan motor used to cool the amplifier has stopped or is operating abnormally. The internal cooling fan helps remove heat from inside the servo amplifier. If the fan is not installed, not inserted correctly, blocked by foreign objects, contaminated by oil or dust, or physically damaged, the amplifier may detect a cooling fan failure and generate the SV0444 alarm. SV0444 is usually related to the internal cooling fan... Read more...
FANUC SV0443 Alarm: Inverter Cooling Fan Failure
The FANUC SV0443 alarm indicates an inverter cooling fan failure. This alarm occurs when the system detects an abnormal condition in the internal cooling fan of the amplifier or power supply module. In many FANUC servo systems, the power supply module or amplifier uses an internal cooling fan to remove heat from the module. If the fan is not installed, not connected correctly, blocked by contamination, or damaged, the module may report SV0443 to protect the drive system from overheating. According to the troubleshooting condition, this alarm may be related... Read more...
FANUC SV0442 Alarm: DC Link Charging Abnormal in Inverter
The FANUC SV0442 alarm indicates a DC link charging abnormal condition in the inverter. This alarm occurs when the common power supply detects an abnormal condition in the DC link backup discharge circuit or when the drive cannot charge the main circuit within the specified time after emergency stop is released. In a FANUC servo system, the DC link circuit must be charged correctly after the machine power sequence is enabled. If the main power is not supplied in time, the voltage is insufficient, the phase sequence is incorrect, the... Read more...
FANUC SV0441 Alarm: Abnormal Current Offset
The FANUC SV0441 alarm indicates an abnormal current offset. This alarm occurs when the digital servo software detects an abnormal condition in the motor current detection circuit. The motor current detection circuit is used by the servo amplifier to monitor the current supplied to the servo motor. If the detected current signal is abnormal, offset, or outside the expected condition, the CNC system may generate the SV0441 alarm. In many cases, this alarm is related to servo amplifier hardware failure. If the amplifier current detection circuit is damaged, the alarm... Read more...
FANUC SV0440 Alarm: Excessive Deceleration Power
FANUC SV0440 Alarm: Excessive Deceleration Power
The FANUC SV0440 alarm indicates that the deceleration power is too large. This alarm occurs when the regenerative discharge amount of the common power supply or servo amplifier becomes excessive,... Read more...
FANUC SV0439 Alarm: Inverter DC Link Overvoltage
The FANUC SV0439 alarm indicates an inverter DC link overvoltage condition. This alarm occurs when the voltage of the DC section of the main circuit, also called the DC bus or DC link, becomes abnormally high. In a FANUC servo system, the servo amplifier and common power supply require stable main circuit voltage. If the DC link voltage rises above the allowable range, the CNC system may generate the SV0439 alarm to protect the servo amplifier, common power supply module, and connected servo system. This alarm may be caused by... Read more...
FANUC SV0438 Alarm: Inverter Current Abnormal
The FANUC SV0438 alarm indicates an inverter current abnormal condition. This alarm occurs when the CNC system detects abnormal motor current or excessive current in the servo motor circuit. In normal servo operation, the motor current should remain within the allowable range for the servo motor, servo amplifier, and machine load condition. If the motor current becomes too high, or if the servo amplifier detects an abnormal current condition, the system may generate the SV0438 alarm. This alarm may be caused by abnormal machining load, excessive acceleration or deceleration, incorrect... Read more...
FANUC SV0437 Alarm: Inverter Input Circuit Overcurrent
The FANUC SV0437 alarm indicates an inverter input circuit overcurrent condition. This alarm occurs when overcurrent is detected in the input circuit of the common power supply, also called the PS module. In a FANUC servo system, the common power supply module supplies power to the servo amplifier system. If excessive current flows into the main input circuit of the common power supply, the CNC system may generate the SV0437 alarm. In some cases, the common power supply may display alarm code 1. This alarm may be related to insufficient... Read more...
FANUC SV0436 Alarm: Soft Thermal Relay Alarm OVC
FANUC SV0436 Alarm: Soft Thermal Relay Alarm OVC
The FANUC SV0436 alarm indicates a soft thermal relay alarm, also known as an OVC alarm. This is a protective alarm detected by the digital servo software when the system... Read more...

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