Technician operating FANUC CNC testing benches during system inspection and repair at REACO CNC.

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 SP9053 SSPA:53 ITP Fault 2 and Troubleshooting
FANUC SP9053 means that the ITP synchronization signal stopped in the communication data exchanged between the CNC and the spindle amplifier. The CNC normally displays SP9053 / SSPA:53 ITP FAULT 2, while the applicable spindle amplifier or combined drive displays 53. FANUC specifies a two-stage hardware repair. First replace the spindle amplifier control printed-circuit board or the complete applicable spindle amplifier. If SP9053 remains after the amplifier side has been correctly replaced, replace the CNC board or module responsible for the serial spindle interface. On the Series 0i-MODEL D and... Read more...
FANUC SP9052 SSPA:52 ITP Fault 1 and Troubleshooting
FANUC SP9052 means that the synchronization signal identified as ITP stopped in the communication data transferred between the CNC and the spindle amplifier. The CNC typically displays SP9052 / SSPA:52 ITP FAULT 1, and the applicable spindle amplifier displays 52. FANUC's repair sequence is hardware-focused. For applicable Series 0i-MODEL D and 0i Mate-MODEL D systems, the maintenance manual first directs technicians to replace the spindle amplifier control printed-circuit board. If the alarm remains, it directs them to replace the CNC main board or sub-CPU board. Other FANUC drive manuals express... Read more...
FANUC SP9051 Alarm 51: DC Link Undervoltage and Troubleshooting
FANUC SP9051 means that the DC-link voltage in the converter main circuit dropped below the required level. Depending on the CNC and drive generation, the CNC may display SP9051 / SSPA:51 LOW VOLT POWER CIRCUIT or a similar DC-link undervoltage message. On applicable serial spindle systems, the spindle amplifier displays 51, while the common Power Supply or PSM normally displays 4 or 04. FANUC identifies an input-voltage drop as the basic cause. The official 0i-D maintenance procedure instructs technicians to check and correct the supply voltage and replace the magnetic... Read more...
FANUC SP9050 Alarm 50: Excessive Speed Calculation in Spindle Synchronization
FANUC SP9050 means that an internal speed-command calculation exceeded its allowable range during spindle synchronous control. The CNC may display SP9050 or SSPA:50 SYNCRONOUS VALUE IS OVER SPEED, while the spindle amplifier displays 50. The basic 0i-D alarm description tells technicians to check whether the specified spindle speed multiplied by the active spindle-to-motor gear ratio exceeds the maximum motor speed. FANUC's detailed αi- and βi-series amplifier manuals add a second branch: if the gear-ratio data is correct, check the spindle-synchronization position gain. For the applicable systems, FANUC instructs technicians to... Read more...
FANUC SP9049 Alarm 49: Differential Speed Is Over Value
FANUC SP9049 means that, during differential spindle speed control, the speed received from the other spindle and converted for the local spindle exceeds the allowable motor-speed limit. The CNC may display SP9049 or SSPA:49 DEF. SPEED IS OVER VALUE, while the spindle amplifier displays 49. FANUC calculates the converted differential-speed component by applying the active local spindle-to-motor gear ratio to the other, normally master-side, spindle speed. The correct response is to verify the commanded speed, motor-specific parameter data, active mechanical gear, and corresponding gear-ratio parameter. Do not increase a motor... Read more...
FANUC SP9047 Alarm 47: Position Coder Signal Error and Troubleshooting
FANUC SP9047 means that the spindle amplifier detected an abnormal pulse count from the spindle position coder. The CNC may display SP9047, SSPA:47, or ILLEGAL SIGNAL OF POSITION CODER, while the spindle amplifier displays alarm 47. For the α position coder configuration described by FANUC, the A/B phase feedback is equivalent to 4096 pulses per spindle revolution. Each time the one-rotation reference signal occurs, the spindle amplifier checks the A/B pulse count accumulated for that revolution. Alarm 47 is issued when the count is outside the specified range. Alarm location... Read more...
FANUC SP9046 Alarm 46: Threading One-Revolution Signal Error and Troubleshooting
FANUC SP9046 means that the spindle amplifier could not detect the position detector's one-revolution signal normally during thread cutting. The CNC may display SP9046, SSPA:46, or ILLEGAL 1REV SIGN OF SCREW CUT, while the spindle amplifier displays alarm 46. FANUC Series 0i-D Maintenance Manual B-64305EN/03 directs technicians to check and correct the applicable parameter, replace the feedback cable, and readjust the BZ sensor signal. FANUC αi Series Maintenance Manual B-65285EN/04 adds an important instruction: troubleshoot alarm 46 by following the alarm 41 procedure. That procedure includes checking the detector settings,... Read more...
FANUC SP9043 Alarm 43: Differential-Speed Position Coder Disconnection
FANUC SP9043 means that the position-coder signal from the master spindle used for differential spindle speed control has been disconnected or detected as abnormal. The CNC may display SP9043 or SSPA:43 DISCONNECT POSITION CODER DEF. SPEED, while the spindle amplifier displays 43. On applicable systems using Submodule SW, FANUC identifies the monitored differential-speed signal at connector JYA3S. The first repair direction is to inspect the position-coder feedback path and replace a defective cable. The spindle amplifier or its control PCB is considered only after the external signal path, connector condition,... Read more...
FANUC SV0741 / SP0741 Rigid Tap Alarm: Excess Error and Troubleshooting
FANUC SV0741, SP0741, or alarm 741 means that either the moving spindle's position deviation or the rigid-tapping synchronization error exceeded its permitted value. Depending on the CNC generation and alarm-prefix convention, the control may display SV0741, SP0741, or simply 741 RIGID TAP ALARM: EXCESS ERROR. FANUC identifies two separate detection conditions for this alarm. The spindle position deviation during movement may exceed the setting of parameter 5311, or the synchronization error between the spindle and tapping axis may exceed parameter 5214. On applicable older systems using separate second-spindle data, the... Read more...
FANUC SV0740 / SP0740 Rigid Tap Alarm: Excess Error and Troubleshooting
FANUC SV0740, SP0740, or alarm 740 means that the spindle position deviation exceeded the permitted stop-state value during rigid tapping. Depending on the CNC generation and alarm-prefix convention, the display may use SV0740, SP0740, or simply 740 RIGID TAP ALARM: EXCESS ERROR. FANUC alarm documentation distinguishes alarm 740 from the adjacent alarm 741. Alarm 740 is generated when the positional deviation of the stopped spindle exceeds its limit during rigid tapping. Alarm 741 is associated with excessive spindle deviation during movement or, on applicable systems, excessive rigid-tapping synchronization error. Alarm... Read more...
FANUC SV0411 Alarm: Excess Error During Movement and Troubleshooting
FANUC SV0411 means that the absolute value of a servo axis's position deviation exceeded the applicable limit while the axis was moving. On many FANUC controls, the English alarm text is SV0411 EXCESS ERROR (MOVING), with the affected axis shown in parentheses. The CNC calculates position deviation from the movement command and position feedback. A normal moving axis has some following error, but the value must remain below the movement limit. For an ordinary servo axis, the relevant limit is generally parameter 1828. During rigid tapping, a separate tapping-axis movement... Read more...
FANUC SV0410 Alarm: Excess Error at Stop and Troubleshooting
FANUC SV0410 means that the absolute value of a servo axis's position deviation exceeded the applicable limit while the CNC judged the axis to be stopped. On many FANUC systems, the English alarm text is SV0410 EXCESS ERROR (STOP), with the affected axis shown in the alarm message. The first diagnostic decision is whether the alarm occurred during an ordinary servo-axis stop or while a tapping axis was stopped in rigid tapping. These conditions can use different limit parameters. For a normal servo axis, the relevant limit is generally parameter... Read more...

Related Resources

Explore more technical materials to help you troubleshoot, maintain, and optimize your CNC system.

Related Links List：

Back to Main Technical Support
Close-up of a CNC machine cutting aluminum parts with high precision.

Need Technical Support or Repairs?

We offer repair services for all CNC parts, including systems, drives, motors, encoders, and PCBs. Fast repair, full testing, and REACO CNC warranty included. Contact us for guidance, troubleshooting, parameter support or repair.

 Tech Support