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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 SP9033 Alarm 33: DC Link Charge Failure and Troubleshooting
FANUC SP9033 means that the DC power voltage in the power circuit was not charged sufficiently when the magnetic contactor turned on. The CNC displays SP9033 / SSPA:33 SHORTAGE POWER CHARGE, the spindle amplifier displays 33, and the common Power Supply (PS/PSM) normally displays alarm 5. FANUC lists an open input phase and a defective charging resistor as example causes. Depending on the installed power-supply series, the detailed procedure may also include the input voltage, magnetic contactor and breaker, power-supply monitor connector CX48, PMC contactor timing, number of connected spindle... Read more...
FANUC SP9032 Alarm 32: Serial Communication LSI RAM Fault
FANUC SP9032 means that the spindle amplifier detected an abnormality in the memory used by its serial communication LSI. The CNC displays SP9032 / SSPA:32 SIC-LSI RAM FAULT, while the spindle amplifier displays 32. FANUC states that this memory check is performed when power is turned on. The official repair direction is to replace the spindle amplifier control printed circuit board or the complete spindle amplifier, depending on the applicable amplifier design and service procedure. Alarm location Typical display Meaning CNC SP9032 / SSPA:32 SIC-LSI RAM FAULT A spindle amplifier... Read more...
FANUC SP9031 Alarm 31: Motor Lock or Detector Signal Loss
FANUC SP9031 means that the spindle motor failed to rotate as commanded and either stopped or remained at a very low speed. The CNC displays SP9031 / SSPA:31 MOTOR LOCK OR DISCONNECT DETECTOR, while the spindle amplifier displays 31. This alarm does not by itself prove that the motor sensor is defective. The same speed-response failure can be produced by excessive mechanical load, a spindle that remains locked, incorrect motor phase sequence, incorrect speed-detector parameters, crossed phase A/B feedback signals, a damaged feedback cable, an open motor power circuit, an... Read more...
FANUC SP9030 Alarm 30: Input Circuit Overcurrent Troubleshooting
FANUC SP9030 means that the spindle system received an input-circuit overcurrent alarm from the common power supply or converter section. The CNC typically displays SP9030 / SSPA:30 OVERCURRENT INPUT CIRCUIT, the spindle amplifier reports 30, and the separate FANUC Power Supply (PS or PSM) normally displays 1. This is primarily a common-power-supply input fault, not a spindle motor overload alarm. FANUC identifies an unbalanced input supply and an incorrectly selected Power Supply whose maximum output specification is exceeded as principal diagnostic directions. The applicable amplifier maintenance manual adds power-unit-specific checks,... Read more...
FANUC SP9029 Alarm 29: Short-Time Overload Troubleshooting
FANUC SP9029 means that an excessive spindle load remained above the configured overload level for the configured detection period. On applicable FANUC controls, the CNC shows SP9029 / SSPA:29 OVERLOAD, while the spindle amplifier displays 29. In the standard setting described by FANUC, alarm 29 is generated when the load-meter reading remains at approximately 9 V for 30 seconds. These are standard values, not universal values for every machine. The actual detection level and time depend on the spindle system parameters and machine configuration. Alarm location Display Meaning CNC SP9029... Read more...
FANUC SP9027 Alarm 27: Position Coder Signal Disconnection Troubleshooting
FANUC SP9027 means that the spindle amplifier detected a disconnected or abnormal αi position coder signal. On a FANUC Series 0i-D/0i Mate-D, the CNC may show SP9027 / SSPA:27 DISCONNECT POSITION CODER, while the spindle amplifier displays 27. FANUC separates the diagnosis according to when the alarm occurs: while the motor is deactivated, when the feedback cable is moved, or while the spindle is rotating. This timing helps distinguish an incorrect sensor setting or permanent open circuit from an intermittent conductor fault or an electrical-noise problem. Alarm location Display Meaning... Read more...
FANUC SP9024 Alarm 24: Serial Transfer Error Troubleshooting
FANUC SP9024 means that an error was detected in serial communication data transferred between the CNC and the spindle amplifier. The CNC may show SP9024 / SSPA:24 SERIAL TRANSFER ERROR, while the spindle amplifier displays 24. There is one important exception: FANUC states that alarm 24 can also appear when the CNC power is off. If it appears only during normal CNC power-off, it does not indicate a failure. If the CNC is powered normally and the alarm remains, check the CNC-to-spindle communication path, cable routing and electrical noise before... Read more...
FANUC SP9022 Alarm 22: Spindle Amplifier Overload Current Troubleshooting
FANUC SP9022 means that current exceeding the spindle amplifier's time rating continued to flow. The CNC displays SP9022 or a series-dependent serial spindle alarm, while the spindle amplifier displays alarm 22. FANUC identifies frequent acceleration and deceleration and a high cutting load as typical causes. The correct first response is to reduce the operating load and verify the spindle motor parameters. For a dual-winding motor, the applicable motor parameters and the winding-switching section of the PMC ladder must also be checked. Alarm location Display Meaning CNC SP9022 / SP AMP... Read more...
FANUC SP9021 Alarm 21: Position Sensor Polarity Error and Troubleshooting
FANUC SP9021 means that the polarity specified for the spindle position sensor does not match the machine configuration. The CNC may display SP9021 or a series-dependent serial spindle alarm, while the spindle amplifier displays 21. FANUC CNC alarm lists instruct technicians to check and correct parameter 4000#0 and parameter 4001#4. The αi Series spindle amplifier maintenance manual also instructs technicians to check the position sensor feedback cable. Alarm location Display Meaning CNC SP9021 / POS SENSOR POLARITY ERROR The configured position sensor polarity is incorrect Spindle amplifier 21 Position sensor... Read more...
FANUC SP9020 Alarm 20: V-Phase Current Offset Causes and Troubleshooting
FANUC SP9020 means that the offset voltage in the spindle amplifier's V-phase current detection circuit is excessively high. On CNC systems that use this alarm mapping, the CNC displays SP9020, while the spindle amplifier displays alarm 20. FANUC maintenance manuals state that this offset check is performed when power is turned on. The normal repair direction is to replace the spindle amplifier module. If alarm 20 appears immediately after the spindle amplifier control printed-circuit board was replaced, check the connectors between the power unit and the control board before replacing... Read more...
FANUC SP9019 Alarm 19: U-Phase Current Offset Causes and Troubleshooting
FANUC SP9019 indicates that the offset voltage in the spindle amplifier's U-phase current detection circuit is excessively high. On systems that use this CNC alarm mapping, the CNC displays SP9019, while the spindle amplifier displays alarm 19. FANUC maintenance manuals state that the offset check is performed when power is turned on. For an αi spindle amplifier module, the standard action is to replace the spindle amplifier. If alarm 19 appears immediately after its control printed-circuit board was replaced, check the connectors between the power unit and the control board.... Read more...
FANUC SP9018 Alarm 18: Program ROM Checksum Error and Troubleshooting
FANUC SP9018 indicates that the spindle amplifier detected an abnormal program ROM sum check. The spindle amplifier displays alarm 18. Depending on the CNC series and software, the CNC may show SP9018, another mapped spindle alarm number, or a general serial spindle alarm. FANUC Maintenance Manual B-65285EN/04 describes alarm code 18 as “A sum check is abnormal.” The specified action is to replace the spindle amplifier or its control printed-circuit board. This is an internal amplifier hardware or program-ROM integrity fault; FANUC does not list a spindle parameter, motor, feedback... Read more...

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