FANUC SP9015 means that the required sequence was not completed correctly during spindle switching or output switching control. The spindle amplifier displays alarm 15.
The alarm is normally issued when a switching request or reference signal changes but the corresponding magnetic-contactor status signal does not change within one second. The main diagnostic areas are the PMC or ladder sequence, magnetic contactor or power-lead switching unit, contactor power supply, feedback wiring, and I/O unit.
| Alarm location | Display | Meaning |
|---|---|---|
| CNC | SP9015 | Spindle switching or output switching sequence error |
| Spindle amplifier | 15 | The expected contactor status transition was not detected within the permitted switching time |
| Main check area | Switching circuit | PMC sequence, contactor operation, feedback signals, wiring, and I/O |
For the surrounding spindle alarm numbers, see the FANUC Serial Spindle Alarm Codes SP9001–SP9033.
What Causes FANUC SP9015?
In FANUC output switching and spindle switching systems, the control must see the correct contactor status after it requests a circuit change. Alarm 15 is generated if the expected transition is not completed within one second.
The exact signal names depend on the FANUC series, software, and switching configuration. FANUC documentation describes the checks as follows:
| Switching function | Request or reference transition | Expected status transition | Alarm condition |
| Output or power-lead switching | RSL, or RCHP in documentation that describes the sequence from this signal | RCH or RCHHG | The applicable contactor status signal does not change within one second |
| Spindle switching | SPSL | MCFN or MFNHG | The applicable contactor status signal does not change within one second |
FANUC Maintenance Manual B-65285EN/03 expresses the general rule as the transition of SPSL or RSL followed by the transition of MCFN, MFNHG, RCH, or RCHHG. Other FANUC documentation separates output switching and spindle switching and describes the output-switching sequence using RCHP. Use the signal table and ladder documentation for the exact CNC and spindle software installed on the machine.
Do not force a signal or bypass the contactor feedback check. The feedback confirms that the power circuit has reached the commanded state before the spindle is energized.
1. Confirm When the Alarm Occurs
Before changing the ladder or any parameter, record:
- The CNC alarm number: SP9015
- The spindle amplifier display: 15
- The exact CNC and spindle amplifier models
- Whether the machine uses output switching, high/low winding switching, or main/sub-spindle switching
- The spindle speed and operating mode when the alarm occurs
- Whether the alarm appears during a switching command or while the spindle appears to be rotating normally
- Whether a contactor, I/O unit, spindle amplifier, motor, or ladder program was recently replaced or modified
Monitor the applicable request, status, and completion signals in the PMC or spindle diagnostic screen. The objective is to identify which requested transition is missing or delayed, not simply to reset the alarm.
2. Check the PMC or Ladder Switching Sequence
If SP9015 occurs during output switching or spindle switching, check the ladder sequence first. Confirm that the sequence:
- Removes spindle excitation as required before power-lead switching
- Commands the correct magnetic contactor or switching unit
- Prevents incompatible contactors from being energized together
- Allows the physical contactor enough time to release or engage
- Receives the correct auxiliary-contact feedback
- Completes the required status transition within one second
- Does not issue the next spindle command before switching is confirmed
Compare the real signal timing with the sequence chart in the applicable FANUC spindle parameter manual and the machine builder’s ladder documentation. If the request changes correctly but the feedback never changes, continue with the contactor, wiring, and I/O checks. If the request itself is incorrect or the commands overlap, correct the PMC or ladder sequence.
Only qualified personnel with the original machine documentation and a verified backup should modify the ladder. An incorrect spindle switching sequence can energize the wrong power circuit or cause two contactors to overlap.
3. Check the Magnetic Contactor and Switching Unit
Inspect the magnetic contactor or power-lead switching unit used for the affected function.
Check:
- Whether the contactor coil receives its specified control voltage when commanded
- Whether the contactor pulls in and releases mechanically
- Whether the main contacts are stuck, worn, or damaged
- Whether the auxiliary contact used for status confirmation changes correctly
- Whether mechanical interlocks prevent the commanded movement
- Whether the switching unit connectors and terminals are secure
If the contactor does not operate, check its power supply and control circuit. If the correct coil voltage is present but the contactor remains inoperative, replace the defective magnetic contactor or applicable power-lead switching unit.
De-energize and isolate the machine before inspecting the power circuit. Spindle switching contactors are connected to hazardous voltages and should be serviced only by qualified personnel.
4. Check the Feedback Wiring and I/O Unit
The contactor may switch physically while SP9015 remains because the amplifier or PMC does not receive the corresponding status confirmation.
Trace the applicable feedback path for MCFN, MFNHG, RCH, or RCHHG and check:
- Auxiliary-contact wiring
- Loose, reversed, or broken conductors
- Connector seating and terminal condition
- Incorrect contact logic or wiring after maintenance
- I/O input voltage and input-state indication
- The I/O channel used by the ladder
Compare the physical contactor state with the I/O signal shown on the diagnostic screen. If the contactor changes but the I/O bit does not, diagnose the auxiliary contact, wiring, connector, and I/O input channel. Repair or replace the defective wiring. Replace the I/O unit only after the wiring and field signal have been verified.
5. When Parameter P4160 May Be Relevant
If SP9015 occurs while the spindle appears to be rotating normally or repeatedly near the speed-range switching point, determine whether the machine uses the speed detection signal SDT for speed-range or output switching.
Parameter P4160 is the speed detection level hysteresis setting. It is not the one-second switching timer. FANUC specifies increasing this value when the SDT-based switching circuit is likely to chatter because the motor speed fluctuates close to the speed detection level.
FANUC parameter documentation states that the hysteresis should be based on the measured speed change during switching, with an appropriate margin. The unit, valid range, standard setting, and related parameter number can vary with the CNC series and parameter increment setting.
Therefore:
- Do not increase P4160 before checking whether SDT is actually used in the switching sequence.
- Do not use P4160 to mask a slow, stuck, or defective contactor.
- Do not use P4160 to compensate for broken feedback wiring or an incorrect ladder sequence.
- Back up the current parameters and use the applicable FANUC parameter manual before making any change.
- Have qualified personnel measure the speed fluctuation and calculate the required hysteresis instead of entering an arbitrary value.
If the alarm is caused by contactor chatter near the switching speed, a correctly calculated increase may stabilize the SDT transition. If the alarm occurs every time a contactor is commanded, diagnose the hardware and sequence first.
6. Retest the Complete Switching Sequence
After correcting the confirmed fault, test the machine at low risk under controlled conditions. Observe the request and status signals through a complete switch in both directions.
Confirm that:
- The correct contactor releases before the other contactor engages
- The expected status signal follows the request within one second
- The signal does not chatter near the switching speed
- The spindle is not energized until switching is complete
- SP9015 does not recur during repeated switching operations
Do not replace the spindle amplifier solely because alarm 15 is displayed. FANUC’s primary alarm 15 procedure focuses on the magnetic contactor or switching unit, status-confirmation wiring, I/O unit, and sequence. Test amplifier-side control hardware only after these external checks are normal and the applicable manual or measured signals indicate an amplifier fault.
SP9015 During Winding Switching and Related Alarms
If SP9015 occurs during high/low winding or output switching, incorrect contactor operation can sometimes be accompanied by another power-circuit alarm. If the spindle amplifier also reports overcurrent during the same transition, use the FANUC SP9012 Alarm 12 troubleshooting guide to check the related overcurrent condition. Diagnose each confirmed alarm; do not assume that SP9012 and SP9015 have the same cause.
Alarm 15 should also be distinguished from amplifier alarm 55:
| Amplifier alarm | FANUC description | Main distinction |
| 15 | The required status transition is not completed within the switching interval | Diagnose the switching action, contactor response, feedback circuit, and ladder timing |
| 55 | The switching request and power-lead status remain inconsistent while the motor is activated | Diagnose a continuing request/status mismatch during motor activation |
Always diagnose the number actually shown on the spindle amplifier.
FANUC SP9015 Diagnostic Table
| Finding | Likely diagnostic direction | Recommended action |
| Request signal does not change correctly | PMC or ladder sequence error | Review and correct the machine switching sequence |
| Request changes, but contactor does not operate | Missing coil power, defective contactor, or switching-unit fault | Check the contactor power supply and control circuit; replace the confirmed faulty unit |
| Contactor operates, but status signal does not change | Auxiliary contact, feedback wiring, connector, or I/O fault | Compare physical state with the diagnostic bit; repair wiring or replace the confirmed faulty I/O component |
| Feedback changes, but takes more than one second | Slow contactor, mechanical problem, or sequence delay | Inspect the contactor and timing; correct the cause of the delayed transition |
| Alarm repeats close to the switching speed and SDT chatters | Insufficient speed detection hysteresis may be involved | Verify SDT use and calculate P4160 according to the applicable FANUC parameter manual |
| Alarm occurs during winding switching together with overcurrent | Switching hardware or sequence may be creating an abnormal current condition | Diagnose both alarm 15 and the related overcurrent alarm |
| External sequence and hardware checks are normal | Further model-specific control diagnosis is required | Check the exact FANUC manual and professionally test the spindle control system |
Recommended Troubleshooting Order
- Confirm SP9015 on the CNC and alarm 15 on the spindle amplifier.
- Identify whether the machine uses output switching, winding switching, or spindle switching.
- Record the exact request and status signals used by the installed FANUC series.
- Monitor the signal transitions and determine which transition is missing or delayed.
- Check the PMC or ladder switching sequence.
- Check the magnetic contactor, switching unit, interlock, and contactor power supply.
- Check the auxiliary contact, feedback wiring, connectors, and I/O input.
- If the alarm occurs near the speed switching point, verify whether SDT chatters and evaluate P4160 using the applicable parameter manual.
- Retest switching in both directions and confirm completion within one second.
- Perform model-specific amplifier diagnosis only if the switching hardware, I/O feedback, and sequence are all confirmed normal.
Technical References
- FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285 series, Alarm Code 15
- FANUC AC Spindle Motor αi/βi Series Parameter Manual, B-65280 series, output switching control, spindle switching control, and P4160
Always use the manual edition that applies to the exact CNC, spindle software, spindle amplifier, motor, switching unit, and machine ladder configuration.
Need Help With FANUC SP9015 Alarm?
REACO CNC provides independent FANUC spindle alarm analysis, spindle amplifier testing and repair, and replacement support. Send us the CNC alarm screen, spindle amplifier display, exact CNC and amplifier models, machine switching function, PMC signal states, ladder timing information, and a description of when the alarm occurs.
Visit the FANUC Technical Support Center for more FANUC alarm guides, or contact REACO CNC for assistance.
Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The applicable signal names, parameter addresses, and procedure depend on the exact CNC series, spindle amplifier, software, and machine configuration.
