FANUC SP9046 Alarm 46: Threading One-Revolution Signal Error and Troubleshooting

September 11, 2026

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, observing the position-coder Z signal, verifying shielding and cable separation, and testing the spindle amplifier only after the external feedback path has been checked.

Alarm location	Typical display	Meaning
CNC	SP9046 / SSPA:46	The one-revolution reference signal was abnormal during threading
CNC message	ILLEGAL 1REV SIGN OF SCREW CUT	FANUC's abbreviated English alarm text for the same condition
Spindle amplifier	46	One-revolution signal detection error during thread cutting
Main diagnostic direction	Detector setting, Z/one-turn signal, cable, shielding, sensor and amplifier	Identify the installed feedback system before changing parameters or replacing parts

For the surrounding spindle alarm numbers, see the FANUC Spindle Alarm Codes SP9034–SP9092.

Safety Warning Before Troubleshooting SP9046

Diagnosing a spindle reference signal may require controlled spindle rotation, a FANUC check board or SERVO GUIDE, or an oscilloscope connected only at an approved test point. Qualified personnel must use the exact FANUC manual, machine drawing, and builder procedure.

Do not probe amplifier connectors with improvised leads, defeat the alarm, or repeatedly cut a thread to reproduce it. Isolate power and observe the DC-link discharge time before opening the feedback circuit. Back up all CNC, PMC, and spindle parameters before changing detector, ratio, or reference data.

What Does FANUC SP9046 Mean?

Thread cutting requires the tool motion to remain synchronized with the spindle's angular position. In a supported threading cycle, the position coder supplies spindle-motion information, and a one-turn reference allows repeated passes to start at a consistent angular position. FANUC detects SP9046 when that one-revolution event cannot be recognized normally during the threading operation.

The abbreviation PC in some translated alarm titles means position coder. It does not mean a personal computer or the spindle amplifier's printed-circuit board. The one-revolution event is commonly associated with the position coder's Z phase, but the actual source can be a position coder, an αi BZ/MZ spindle sensor, or an external one-revolution detector, depending on the machine.

SP9046 does not prove that all spindle feedback has disappeared. Incremental speed feedback may remain normal while the once-per-revolution reference is missing, intermittent, noisy, or inconsistent with the selected detector. The spindle can therefore run in speed control and alarm only when threading begins.

The alarm is not limited to rigid tapping. FANUC's English message says SCREW CUT, and its maintenance description says thread cutting. Diagnose the program actually being executed.

Why the One-Revolution Signal Matters During Threading

During thread cutting, the CNC converts measured spindle motion into synchronized feed. The one-revolution reference gives the control a repeatable angular event for starting successive threading passes at the same point. If that event is absent or cannot be accepted normally, the control cannot guarantee correct thread alignment and stops the operation with alarm 46.

The spindle may therefore rotate normally but alarm at the threading block. Orientation can also fail if it shares the same reference path; however, successful orientation does not exclude an intermittent, speed-dependent, gear-dependent, or vibration-related fault. A stable rpm display likewise does not prove that the once-per-revolution pulse is valid.

1. Confirm SP9046 and Record the Exact Operating Condition

Before changing a parameter, confirm:

The CNC shows SP9046, SSPA:46, or the series-specific alarm-46 text.
The spindle amplifier display shows 46.
The alarm belongs to the correct spindle on a multi-spindle machine.
The alarm occurs during thread cutting rather than ordinary spindle rotation, orientation, rigid tapping, spindle synchronization, or another mode.
Any accompanying spindle or servo alarms have been recorded in their original order.

Record the CNC and amplifier models, spindle software, motor and detector types, connector, gear, speed, program block, and whether the alarm is repeatable. Note any recent parameter restoration, amplifier or encoder replacement, spindle work, belt adjustment, rewiring, or coolant exposure.

The exact timing is particularly useful:

Alarm timing	Most relevant diagnostic direction
Appears immediately when threading is commanded	Detector selection, one-revolution settings, missing Z signal, wrong connector, or open cable
Appears only in one spindle gear	Gear-dependent parameters, mechanical ratio, gear-selection state, or a gear-related cable/mechanical condition
Appears only above or below a certain speed	Signal level, supported low-speed detection setting, noise, sensor clearance, or speed-dependent vibration
Appears when the spindle head or cable carrier moves	Intermittent conductor, loose terminal, damaged strain relief, or contaminated connector
Appears only under cutting load	Vibration, belt/coupling movement, shielding, grounding, or a marginal detector signal

Record intermittent symptoms before disturbing the cable; moving a connector can temporarily hide the failure.

2. Identify the Installed Position-Feedback System

Use the electrical drawing and applicable English FANUC connection manual to determine whether the machine uses:

An αi position coder driven directly by the spindle
A position coder driven through a 1:1 gear or timing belt
An α position coder S
An αi BZ, MZ, or CZ spindle sensor
An external one-revolution proximity switch combined with motor-sensor feedback
A machine-specific switching, multi-spindle, or geared feedback arrangement

JYA3 is common for a position coder or external one-revolution input in applicable configurations, but it is not universal. Other sensors may use JYA2 or JYA4, and switching systems can add intermediate connectors. Trace the actual circuit. Do not apply a BZ procedure to a position coder or an external-switch parameter to a Z-phase configuration.

3. Use Spindle Orientation as a Controlled Diagnostic

If the machine builder permits it, try spindle orientation using the normal machine function under safe conditions. Orientation is useful because many configurations also require a spindle position reference.

Interpret the result carefully:

Orientation result	What it suggests	Next action
Orientation also fails or searches continuously	A common detector, one-revolution signal, parameter, cable, or mechanical-reference problem is likely	Observe the reference signal and verify the installed feedback configuration
Orientation stops at inconsistent positions	The reference event may be noisy, intermittent, mechanically unstable, or incorrectly configured	Check Z/one-turn repeatability, coupling, shielding, and settings
Orientation works consistently	The signal path is not proven good under threading conditions	Continue checking for speed-, gear-, vibration-, and routing-dependent faults

Do not change orientation parameters merely because orientation fails. First compare the data with a known-good backup and exact English parameter manual. Speed, direction, ratio, detector selection, and reference-return settings are configuration-specific.

For systems using an external one-revolution signal, FANUC B-65280EN explains that the reference-position return speed and direction may need to agree with the orientation speed and direction when the same signal is shared. This is a configuration check, not a universal instruction to increase or decrease one parameter.

4. Observe the Z Phase or One-Revolution Signal

FANUC's alarm-41 procedure, which is also specified for alarm 46, directs technicians to observe the position-coder Z signal. If the Z signal is not generated once per rotation after the cable path and settings are verified, the manual directs replacement of the position coder.

Use the approved method for the installed hardware, such as a FANUC check board, supported SERVO GUIDE data, a specified PS/PSD test point, or a documented machine diagnostic.

During a controlled low-speed test, determine:

Whether a one-revolution pulse exists.
Whether exactly one valid event occurs for each expected spindle or coder revolution.
Whether the event occurs at a repeatable angular position.
Whether the pulse level and shape remain stable as speed changes within the approved test range.
Whether the result changes when the cable carrier, connector, belt, or spindle assembly moves.

No signal at the amplifier does not by itself prove that the coder failed. A cable, connector, setting, contamination, or amplifier-input fault can produce the same result.

5. Verify the Applicable Detector and One-Revolution Parameters

FANUC lists an incorrect sensor setting as a possible cause in the alarm-41 procedure used for SP9046. Compare the active spindle parameters with the approved machine backup, the exact detector specification, and the applicable edition of B-65280EN.

The relevant areas can include:

Spindle-sensor or position-coder type
Sensor mounting direction and signal polarity
Standard or arbitrary detector tooth count
Motor-to-spindle and detector-to-spindle mechanical ratio
External one-revolution signal type
Active spindle and gear-range selection
Reference-position return and orientation conditions
Supported low-speed one-revolution detection options

Some B-65280EN configurations use parameter 4004 bits for an external one-revolution signal, parameter 4074 for reference-position return speed, and parameter 4394#2 for a supported low-speed detection selection. These are configuration examples, not a universal SP9046 parameter list.

Do not copy data from a similar-looking machine or initialize all spindle parameters as a first response. Preserve a full backup, correct only verified data, and follow the specified power-cycle procedure.

6. Inspect the Feedback Cable and Connectors

With power safely isolated, inspect the complete detector-to-amplifier circuit, including intermediate plugs and switching modules where fitted. Check for:

A cable connected to the wrong amplifier interface
Connectors that are not fully seated or locked
Bent, recessed, oxidized, or loose contacts
Cuts, abrasion, crushing, heat damage, tight bends, or stretched sections
Broken conductor strands near the connector or cable carrier
Damaged seals, backshells, or strain relief
Repairs that changed the conductor arrangement or interrupted the shield

If the alarm changes when the harness moves, perform an approved continuity and flex test. Replace a damaged, intermittent, incorrectly specified, or poorly shielded cable with the correct FANUC or builder part—not a generic cable with a similar connector.

7. Check for Coolant, Oil, and Connector Contamination

The field procedure supplied for this article includes coolant intrusion as a practical cause. Inspect the position-detector and amplifier-side connectors for coolant, oil, conductive residue, corrosion, or damaged seals.

If contamination is found, isolate power, correct the source, and clean or replace the connector by the hardware-specific procedure. Let it dry fully, inspect the contacts, and restore the seal and strain relief before testing. Do not use an unsuitable cleaner or reconnect a damp plug.

Coolant inspection is a valid field diagnostic branch, but it is not listed as a separate universal alarm-46 remedy in every FANUC manual. It should complement—not replace—the official parameter, signal, cable, and shielding checks.

8. Check the Position Coder Mounting, Belt, and Coupling

When the position coder is mechanically driven from the spindle, verify the physical relationship described by the machine design:

The coder body and mounting bracket are secure.
The shaft coupling, key, gears, and pulley fasteners are not loose.
The timing belt has the specified tension and is not slipping or damaged.
A documented 1:1 coder-to-spindle relationship has not been altered.
The selected gear state agrees with the actual mechanism.
Recent spindle repair did not change detector phase, pulley ratio, or mounting direction.

A slipping belt or loose coupling can leave incremental feedback present while the reference shifts relative to the spindle. Do not rotate the coder, move a switch, or alter mechanical phase by trial and error; use the builder's alignment procedure.

9. Correct Shielding, Grounding, and Cable Routing

FANUC's alarm-41 procedure specifically directs technicians to check the feedback-cable shield and to separate the signal cable from the motor power lead. These checks are especially important when SP9046 occurs only during spindle rotation or under load.

Confirm that:

The specified shielded feedback cable is installed.
The shield is continuous and has not been cut by a repair.
Frame-ground termination uses the specified cable clamp and mounting surface.
The detector cable is separated from spindle-motor, servo-motor, braking, and other high-current cables along the full route.
Excess feedback cable is not coiled beside an amplifier, reactor, contactor, or motor-power cable.
Cabinet and machine-frame grounding points are tight, clean, and consistent with the electrical drawing.

Do not add arbitrary ground wires or change the specified shield termination; an improvised ground can make the signal less reliable.

10. Readjust a BZ Sensor Only When That Sensor Is Installed

B-64305EN/03 lists readjustment of the BZ sensor signal as an SP9046 remedy. This instruction applies only when the machine actually uses the corresponding adjustable BZ sensor and the signal test shows that adjustment is required.

Use the detector-specific English procedure, approved test equipment, prescribed speed, and specified waveform limits. Record the original setting. Turning an adjustment until the alarm disappears is not a valid commissioning method.

Do not generalize the BZ instruction to every spindle detector. FANUC documentation states that some αi M/MZ detector signals normally require no adjustment, analog αi CZ sensors are adjusted at shipment and should not be casually readjusted, and some position coders permit only a signal-level check rather than the same BZ adjustment. Identify the exact sensor model first.

If the signal remains outside specification, inspect sensor clearance, mounting, target gear, cable, and amplifier input.

11. Replace the Position Coder or Sensor Only After Isolation

If the approved test proves that the position-coder Z phase is not generated once per revolution, and the correct settings, connector, and cable path have been verified, FANUC's alarm-41 procedure specifies replacement of the position coder.

Before replacement, verify the detector part number, suffix, mounting, connector, cable, and ratio. Preserve the angular relationship and complete the required orientation and threading checks. A new sensor will not correct a cable, parameter, belt, or amplifier-input fault.

12. Test the Spindle Amplifier Last

FANUC's alarm-41 procedure includes replacement of the spindle amplifier or its control printed-circuit board after the sensor settings, Z signal, shielding, and cable routing have been checked. Amplifier-side hardware becomes a reasonable suspect when:

The correct detector configuration and parameters are verified.
A valid, stable one-revolution signal reaches the specified amplifier input.
The cable, connectors, shielding, grounding, and routing are confirmed.
The mechanical detector relationship is stable.
The alarm remains on the same amplifier input.

Use an exact compatible amplifier or control board. Verify the complete part number, suffix, hardware series, spindle software, detector support, and machine options.

If replacement support is required, browse FANUC servo, spindle, and power drives or send REACO CNC the complete amplifier information for compatibility checking.

Difference Between SP9041, SP9042, SP9046, and SP9047

CNC alarm	Amplifier display	FANUC signal condition	Main diagnostic distinction
SP9041	41	Position-coder one-revolution signal occurs at an incorrect position	The reference occurs, but its position or relationship is abnormal
SP9042	42	Position-coder one-revolution signal is not generated	The one-turn reference is missing in the general detection condition
SP9046	46	One-revolution signal cannot be detected normally during thread cutting	The abnormal reference is detected specifically during threading
SP9047	47	Position-coder pulse count or phase relationship is abnormal	Focuses on A/B incremental feedback rather than only the one-turn event

FANUC directs technicians to troubleshoot alarm 46 as alarm 41, but the alarm numbers are not interchangeable. For more detail, see the FANUC SP9041 one-rotation signal error guide and the FANUC SP9042 missing one-rotation signal guide.

FANUC SP9046 Diagnostic Table

Finding	Likely interpretation	Recommended action
Spindle runs normally but SP9046 appears at the threading block	Speed feedback may exist while the one-turn reference is missing or abnormal	Observe the Z/one-revolution signal and verify the threading feedback configuration
Orientation and threading both fail	The functions may share a detector, reference signal, parameter, or cable path	Check the actual signal before changing orientation data
Orientation works but SP9046 remains	The fault may be speed-, gear-, vibration-, or mode-dependent	Test under the approved threading-related speed and active gear condition
No Z/one-turn event reaches the amplifier	Detector, cable, connector, selection parameter, or input circuit may be open	Isolate the cable path before replacing the detector
Z event appears more or less than once per expected revolution	Detector output, mechanical ratio, coupling, tooth count, or signal selection is incorrect	Verify detector configuration and mechanical relationship
Signal becomes unstable when the cable moves	Intermittent conductor, terminal, connector, or strain-relief fault	Flex-test safely and replace the correct cable if confirmed
Alarm occurs only while rotating or under load	Electrical noise, incomplete shield, poor grounding, cable proximity, vibration, or belt movement is likely	Restore approved routing and shielding; inspect the mechanical drive
BZ waveform is outside the specified range	BZ clearance, mounting, adjustment, cable, target, or input may be abnormal	Use the exact BZ adjustment procedure; do not apply it to another detector type
Valid signal reaches the amplifier but alarm 46 remains	Amplifier input or control board may be abnormal	Test with an exact compatible amplifier or board after all external causes are excluded

Recommended Troubleshooting Order

Confirm SP9046/SSPA:46 on the CNC and 46 on the spindle amplifier.
Record the threading block, spindle speed, gear, alarm timing, CNC, amplifier, software, and detector details.
Identify the actual position coder, BZ/MZ/CZ sensor, or external one-revolution detector and trace its complete connector path.
Use spindle orientation only as a controlled diagnostic; do not change orientation parameters without verified data.
Observe the Z phase or one-revolution event using the approved FANUC test method.
Compare detector, ratio, one-revolution, and reference settings with a known-good backup and the applicable B-65280EN manual.
Isolate power and inspect every connector, cable section, seal, contact, and strain relief.
Check the coder mounting, coupling, pulley, timing belt, and actual gear relationship.
Restore the specified cable shield, frame-ground termination, and separation from motor power wiring.
If an adjustable BZ sensor is installed, test and readjust it only by the detector-specific procedure.
Replace the position coder or sensor only when signal testing isolates it as defective.
Replace the exact compatible spindle amplifier or control PCB only after the external feedback circuit is proven normal.
Retest orientation and thread cutting at the machine-builder-specified safe conditions before returning the machine to production.

Technical References

FANUC Series 0i-MODEL D / 0i Mate-MODEL D Maintenance Manual, B-64305EN/03, SP9046 / SSPA:46
FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Alarm Codes 41 and 46 and spindle-feedback signal checking
FANUC AC Spindle Motor αi Series / βi Series / Built-in Spindle Motor Bi Series Parameter Manual, B-65280EN/05, position detector, one-revolution signal, reference-position return, and orientation settings
FANUC Servo Amplifier αi Series Descriptions, B-65282EN/06, spindle-feedback connections, cable shielding, and grounding
FANUC Series 0i-MODEL D / 0i Mate-MODEL D User's Manual (Machining Center System), B-64304EN-2/01, threading synchronization and one-turn signal operation

Always use the English manual edition that applies to the exact CNC, spindle amplifier, spindle software, detector, and machine configuration. Parameter numbers, test points, connectors, and adjustment procedures can differ by hardware and software series.

Need Help With FANUC SP9046 Alarm 46?

REACO CNC provides independent troubleshooting, testing, repair, compatibility checking, and replacement support for FANUC spindle amplifiers and feedback systems. Send us the CNC alarm screen, amplifier display, complete CNC model, exact spindle amplifier model and suffix, spindle software information, position-detector model, feedback-cable part number, threading program block, and the condition in which alarm 46 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 English-language FANUC technical documentation. The applicable parameter, signal-test, sensor-adjustment, cable, replacement, and verification procedure depends on the exact CNC, spindle amplifier, spindle software, detector type, and machine.