FANUC SV0475 means that the servo processor detected a moving-axis position deviation greater than the applicable limit in parameter No.1838 or No.1841. This alarm belongs to the position-error monitoring function of FANUC Dual Check Safety. The CNC may display SV0475 EXCESS ERROR (MOVE:SV) together with the affected axis.
| Alarm item | Meaning |
|---|---|
| CNC alarm | SV0475 EXCESS ERROR (MOVE:SV) |
| Detection side | Servo CPU / servo DSP |
| Detection state | The axis is moving |
| Monitored value | Servo following error, also called position deviation |
| Applicable limit | No.1838 when safety monitoring is requested; No.1841 when it is not requested |
| Official first check | Confirm that No.1838 and No.1841 are correctly set and not unnecessarily small |
| Safety response | Alarm output and immediate axis stopping equivalent to an emergency stop on applicable systems |
For a wider alarm-number reference, see the FANUC SV Alarm Codes guide.
What Does FANUC SV0475 Mean?
During axis movement, the CNC sends position commands and receives position feedback from the motor pulse coder or the configured position detector. The difference between commanded position and feedback position is the position deviation, following error, or servo error.
Some following error is normal while an axis accelerates, travels, decelerates, and reverses direction. The amount depends on commanded speed, acceleration, servo-loop response, load, detector resolution, and machine mechanics. SV0475 occurs when the servo-side safety processor determines that the absolute moving-state deviation has exceeded the applicable Dual Check Safety limit.
The alarm therefore reports a monitored condition rather than identifying one failed part. A safety deviation limit that is too small can cause the alarm even when the axis otherwise follows normally. However, excessive real deviation can also result from mechanical binding, a brake that did not release, excessive load, incorrect servo data, unstable feedback, motor-power problems, unsuitable acceleration, or an amplifier fault.
Do not confuse servo following error with finished-part dimensional error. SV0475 does not mean that a machined dimension is simply outside tolerance. It means the controlled axis failed to follow its commanded motion within the permitted safety limit.
How No.1838 and No.1841 Are Selected
The effective moving-state limit depends on the Dual Check Safety monitoring request signal *VLDVx for the affected axis:
| Dual Check Safety state | Signal state | Moving-state limit | Meaning |
|---|---|---|---|
| Safety monitoring is being carried out | *VLDVx = 0 | No.1838 | Moving-axis position-deviation limit during the safety check |
| Safety monitoring is not being carried out | *VLDVx = 1 | No.1841 | Moving-axis position-deviation limit outside the active safety-monitoring state |
On the systems covered by FANUC B-64004EN/02, No.1838 and No.1841 are two-word, axis-type parameters specified in detector units. The documented range is 0 to 99,999,999, but the correct value is machine-specific and must be established from the machine's detector resolution, servo behavior, motion profile, mechanics, safety design, and risk assessment.
There is an important fallback rule: when No.1841 is set to 0, the manual states that No.1828 becomes the moving-state limit while *VLDVx is 1. When *VLDVx is 0, No.1838 is used.
| Condition when SV0475 occurs | Parameter to verify first |
|---|---|
| Alarm occurs while the safety-monitoring request is active | No.1838 |
| Alarm occurs while the safety-monitoring request is inactive | No.1841 |
| No.1841 is 0 | No.1828, because it becomes the fallback moving-state limit |
| Alarm occurs exactly when the safety state changes | *VLDVx timing, active limit, and the actual deviation at the transition |
| Signal state is uncertain | Use Dual Check diagnosis and the machine ladder documentation before changing data |
No.1838 and No.1841 are not two alternative values that should automatically be increased together. First identify the active signal state and the deviation behavior that produced the alarm.
Do Not Simply Increase the Position-Deviation Limit
FANUC's concise procedure directs technicians to check whether No.1838 and No.1841 are too small. That is a parameter-verification step, not permission to keep increasing a safety limit until the alarm disappears.
A larger value permits more following error before the safety system reacts. If the actual cause is a locked brake, mechanical obstruction, deteriorating motor cable, feedback instability, incorrect servo data, or insufficient drive torque, increasing the limit can conceal a developing failure and allow more uncontrolled deviation.
Before any authorized change:
- Back up the complete CNC, servo, PMC, and Dual Check Safety configuration.
- Record No.1838, No.1841, No.1828, and the original value for every affected axis.
- Confirm the *VLDVx state at the alarm event.
- Record the actual position-deviation behavior during the failing movement.
- Compare the data with a verified machine-builder backup.
- Confirm that the proposed setting remains consistent with the machine's safety calculation and risk assessment.
- Follow the applicable password, authorization, power-cycle, checksum, and acceptance-test procedure.
The cited manual requires power to be turned off before operation continues after these parameters are set. Treat any change as a controlled safety-system modification.
Safety Before Troubleshooting
SV0475 is generated during movement, so an axis may stop suddenly after the safety system detects excessive deviation. Secure the machine, workpiece, tooling, and any vertical or gravity-loaded mechanism before inspection. Do not enter the working area until hazardous energy is isolated and the applicable lockout procedure is complete.
Do not bypass *VLDVx, force safety I/O, defeat a brake, disable Dual Check Safety, or change ladder logic merely to complete a cycle. Powered motion tests and safety-parameter changes must be performed by qualified personnel following the FANUC and machine-builder procedures.
1. Confirm the Complete Alarm and Affected Axis
Record the alarm screen before resetting or switching off the CNC:
- The complete SV0475 EXCESS ERROR (MOVE:SV) message
- The affected axis and machine position
- Whether SV1071, SV0411, a pulse-coder alarm, an overcurrent alarm, or another safety alarm appears simultaneously
- The active operating mode: jog, rapid traverse, cutting feed, reference return, automatic cycle, tool change, or another motion
- Commanded direction, feedrate, rapid override, load, and approximate position
- The CNC series, software, servo amplifier, motor, detector, and brake specifications
- Any recent collision, maintenance, parameter restore, motor replacement, encoder work, drive replacement, or ladder modification
The time and motion phase are often highly diagnostic. An alarm that occurs immediately when motion is commanded has a different likely cause from one that occurs only at maximum rapid speed, under cutting load, at one physical position, or during reversal.
2. Observe How the Position Deviation Becomes Excessive
Use the applicable FANUC diagnostic or servo waveform function under the machine builder's safe test procedure. Determine whether the deviation:
- Rises immediately while the axis fails to move
- Peaks mainly during acceleration
- Becomes excessive only above a certain feedrate
- Increases under cutting or process load
- Spikes at one repeatable physical location
- Changes sharply at reversal or deceleration
- Oscillates with visible or audible vibration
- Becomes abnormal only after the machine warms up
- Changes when a cable carrier, feedback cable, or motor lead moves
This evidence separates a threshold-selection issue from a genuine motion-control problem. If the deviation is large because the axis cannot follow, changing No.1838 or No.1841 changes only when the safety stop occurs.
3. Verify No.1838, No.1841, and the No.1828 Fallback
Compare the active parameters with a verified backup for the exact CNC, detector, axis, and machine. Check the following:
- Confirm the intended No.1838 setting for the affected axis.
- Confirm the intended No.1841 setting outside active safety monitoring.
- If No.1841 is 0, verify the effective fallback value in No.1828.
- Confirm that the values are interpreted in detector units and match the configured detector resolution.
- Review any servo initialization, CNC memory replacement, parameter restore, motor change, detector change, or flexible-feed-gear change.
- Confirm that values were not copied from an axis with different mechanics, speed, inertia, reduction ratio, or resolution.
An unexpectedly small value can explain a nuisance trip during otherwise normal movement. An unexpectedly large value is also a safety concern and should not be accepted merely because the axis runs without an alarm.
4. Check the Safety-Monitoring Request Timing
The technician-supplied recommendation to check position-detection timing is relevant because *VLDVx determines which moving limit is selected. Review the machine ladder, safety design, and Dual Check diagnosis to identify the signal state before, during, and after the failed movement.
Check for:
- A transition from No.1841 to a smaller No.1838 limit while normal moving deviation is still present
- A safety request that changes unexpectedly during acceleration, travel, or deceleration
- Chattering or intermittent guard, door, mode, or safety input signals
- An axis-motion command that remains active during an unintended safety-state transition
- A ladder or safety-I/O change that altered the intended sequence
- A difference between the documented safety sequence and the active PMC logic
Correct timing means restoring the validated machine sequence. It does not mean delaying, forcing, or bypassing a required safety response. Any logic change requires authorization, risk assessment, verification, and the prescribed acceptance test.
5. Check for Mechanical Resistance or Excessive Load
If the deviation is genuinely excessive, inspect the complete mechanical transmission before assuming that an electronic component has failed.
Check for:
- A collision, workpiece, fixture, chip buildup, cover, or other obstruction
- Poor lubrication, tight guideways, a binding ballscrew, damaged bearing, or gearbox problem
- A loose coupling, slipping belt, damaged key, pulley, or transmission component
- Excessive cutting force, unsuitable tooling, or abnormal process pressure
- A counterbalance, hydraulic cylinder, clamp, or rotary mechanism creating excessive resistance
- A fault that repeats at the same machine position
- Excessive load or inertia after a fixture, spindle head, table, or machine component was changed
If the axis does not move after a command, do not keep commanding motion against a possible obstruction. Following error and motor current can rise rapidly while the mechanism remains blocked.
6. Verify That the Brake or Clamp Releases Correctly
A brake or mechanical clamp that remains applied can produce a rapid increase in position deviation as soon as the CNC commands movement. This is especially relevant to vertical, inclined, rotary, and tool-change axes.
Verify the machine builder's release sequence, brake-coil voltage, pneumatic or hydraulic pressure, release feedback, and mechanical action. Look for a brake that releases late, releases only partially, drags when warm, or remains engaged because of an output, relay, wiring, pressure, or mechanical problem.
Do not bypass the brake or remove a safety interlock for a trial. A vertical or gravity-loaded mechanism can fall or move unexpectedly. Support the load and follow the specified brake test procedure.
7. Check Commanded Speed, Acceleration, and Motion Profile
An axis may remain within its deviation limit at low feed but exceed it during rapid acceleration, high-speed travel, reversal, or aggressive deceleration. Confirm:
- Programmed feedrate and rapid override
- Maximum axis speed and acceleration/deceleration settings
- Motor and amplifier capacity for the installed load
- Detector resolution, command multiplier, reduction ratio, and flexible-feed-gear data
- Whether the alarm began after a parameter restore or motion-cycle change
- Whether it occurs only with a heavy workpiece or fixture
If reducing feed or acceleration prevents the alarm, treat that as diagnostic evidence rather than the final repair. Determine why the axis cannot follow the original approved motion profile.
8. Inspect Motor Power, Feedback, and Cable Routing
With machine power isolated and the DC link fully discharged, inspect the affected axis's power and feedback circuits.
For the motor-power circuit, check:
- U/V/W connectors, terminals, cable continuity, and phase balance
- Loose, overheated, broken, crushed, oil-contaminated, or flex-damaged conductors
- Motor winding continuity and insulation using the approved procedure
- Correct axis and amplifier-channel assignment after maintenance
For the feedback circuit, check:
- Pulse-coder or scale connectors, locks, contacts, and contamination
- Cable continuity, shielding, grounding, and flex sections
- Separation from motor, contactor, transformer, and other high-power wiring
- Detector mounting, coupling, and machine-scale alignment where applicable
- Correct detector type and resolution in the active servo data
SV0475 is not a dedicated motor-cable or pulse-coder disconnection alarm. Give these checks priority when there are simultaneous detector or current alarms, implausible diagnostic values, recent wiring work, or a fault that changes as a cable moves.
9. Review Servo Parameters and Control Stability
Incorrect motor identification, detector data, direction, loop gain, load inertia, flexible-feed-gear values, acceleration data, or machine-specific servo tuning can prevent an axis from following correctly.
Compare the complete active servo data with a verified backup. Do not reinitialize the servo merely because SV0475 appears. Initialization can overwrite machine-builder values and introduce additional motion or safety problems.
If the axis vibrates or hunts while moving, inspect mechanical looseness, resonance, detector mounting, load inertia, gain, and filter settings. Do not copy tuning values from another axis or make random gain adjustments. Use waveform and mechanical evidence to distinguish instability from load or feedback problems.
10. Check the Servo-Off and Machine-Control Sequence
If motor excitation is removed while the CNC continues issuing position commands, the axis cannot follow and the deviation can rise rapidly. Review the PMC and safety sequence for an unexpected servo-off request, drive-ready interruption, contactor problem, clamp command, or mode transition during movement.
Do not force the servo-ready or servo-off signals. Identify why the command, excitation, and actual machine state disagree, then correct the responsible field input, output, wiring, ladder condition, or machine component.
11. Use the Dual Check Diagnosis Screen
On applicable FANUC controls, the Dual Check diagnosis screen is available in the SYSTEM group through the DUAL CHECK soft key. It can display safety-related signal states and the cause recorded when a safety alarm occurs.
Record:
- The *VLDVx state for the affected axis
- The alarm source and detection side
- Related safety inputs and outputs
- The state before and after the alarm
- Whether the CNC-side and servo-side monitoring paths report corresponding conditions
Screen names and access steps vary by CNC series and software. Use the applicable manual and do not edit safety data merely because it is visible on a diagnostic screen.
12. Test the Servo Amplifier Only After External Causes Are Checked
An amplifier can cause excessive following error if it cannot produce the commanded current, loses an output phase, processes feedback incorrectly, or controls the motor abnormally. However, SV0475 alone does not prove that the amplifier is defective.
Review all simultaneous alarms and verify the parameters, signal timing, mechanism, brake, load, power wiring, motor, detector, and servo sequence first. If substitution is necessary, use an exact compatible amplifier and preserve the original machine configuration. Match the complete FANUC model and suffix rather than choosing by appearance or output rating alone.
REACO CNC can help test, repair, or select compatible FANUC servo, spindle, and power drives.
SV0475 and Its CNC-Side Pair
Dual Check Safety monitors the same safety-relevant condition through independent CNC and servo paths:
| Detection side | Alarm | Meaning |
|---|---|---|
| Servo CPU / servo DSP | SV0475 | Servo-side moving-position deviation exceeded No.1838 or No.1841 |
| CNC CPU | SV1071 | CNC-side moving-position deviation exceeded No.1838 or No.1841 |
Record both alarms when they appear together. They represent the two monitoring paths and should not be dismissed as duplicate messages. If only one appears, diagnose the exact detection side and the active condition before replacing hardware.
Difference Between SV0475 and Related Excess-Error Alarms
| Alarm | Detection side | Axis state | Applicable limit on the cited system |
|---|---|---|---|
| SV0475 | Servo CPU | Moving | No.1838 or No.1841 |
| SV1071 | CNC CPU | Moving | No.1838 or No.1841 |
| SV0474 | Servo CPU | Stopped | No.1839 or No.1842 |
| SV1072 | CNC CPU | Stopped | No.1839 or No.1842 |
| SV1070 | Servo CPU | Servo off | No.1840 |
| SV1069 | CNC CPU | Servo off | No.1840 |
For the corresponding stopped-state procedure, see the FANUC SV0474 Excess Error at Stop guide.
SV0475 should also be distinguished from SV0411 EXCESS ERROR (MOVING). SV0411 is an ordinary moving-position deviation alarm on applicable systems and commonly references No.1828. SV0475 is the servo-side Dual Check Safety alarm and normally references No.1838 or No.1841. No.1828 becomes directly relevant to SV0475 only when the cited system uses it as the fallback because No.1841 is 0.
FANUC SV0475 Diagnostic Table
| Finding | Interpretation | Recommended action |
|---|---|---|
| No.1838 or No.1841 differs from the verified backup | Safety deviation data may have been altered or restored incorrectly | Preserve the current data and restore only through the authorized safety procedure |
| No.1841 is 0 | No.1828 is the effective moving-state limit while *VLDVx is 1 | Verify No.1828 before assuming that a zero value disables monitoring |
| Alarm occurs exactly when *VLDVx changes | The selected limit and safety-request timing may not match the motion state | Review the signal transition and deviation trace against the validated ladder sequence |
| Deviation rises immediately and the axis does not move | Brake/clamp, blockage, motor-power circuit, servo-off state, or amplifier output may be preventing movement | Stop commanding motion and inspect the mechanism, sequence, and power circuit |
| Alarm occurs only at high rapid speed | Speed, acceleration, load, motor data, available torque, or limit setting may be unsuitable | Verify the approved motion profile and diagnose why following performance falls at higher demand |
| Alarm repeats at one physical position | Local binding, cable-chain damage, scale issue, or transmission defect may be present | Inspect that travel area while comparing load, feedback, and position deviation |
| Alarm began after parameter restore or motor replacement | Motor, detector, ratio, gain, or safety data may not match | Compare the complete configuration with the verified machine backup |
| Alarm changes when a cable moves | Power or feedback wiring may be intermittent | Isolate power and test the affected cable, connector, shielding, and routing |
| SV0475 and SV1071 occur together | Both independent monitoring paths detected excessive moving deviation | Record both and diagnose the real deviation, active limit, and safety state |
| External conditions and configuration are verified | Servo amplifier control or output stage may be faulty | Professionally test or replace the exact compatible amplifier and complete safety validation |
Recommended Troubleshooting Order
- Record the complete SV0475 message, affected axis, motion phase, direction, feedrate, load, and simultaneous alarms.
- Secure the machine and any gravity-loaded mechanism before inspection.
- Preserve the actual position-deviation and safety-signal evidence before repeated resets.
- Determine the *VLDVx state and identify whether No.1838 or No.1841 is active.
- If No.1841 is 0, verify the fallback moving-state limit in No.1828.
- Compare all three values with the verified backup and exact machine safety documentation.
- Review the timing of *VLDVx and any guard, mode, brake, clamp, or servo-state transition.
- Inspect for collision, obstruction, binding, poor lubrication, abnormal load, or a brake that did not release.
- Confirm that commanded speed, acceleration, detector resolution, motor data, and drive capacity match the machine specification.
- With power safely isolated, inspect motor-power and feedback wiring, the motor, detector, shielding, and correct axis assignment.
- Compare servo parameters with the verified backup and diagnose any vibration or instability with waveform evidence.
- Review servo-off, drive-ready, and machine-control logic for an unexpected loss of excitation during movement.
- Use the Dual Check diagnosis screen to confirm the signal state and detection side.
- Test or replace the amplifier only after configuration, sequence, mechanics, load, motor, and external wiring have been checked.
- Retest at a controlled speed and load, then perform the required Dual Check Safety acceptance test before returning the machine to production.
Reset and Post-Repair Verification
The cited manual states that some Dual Check Safety alarms can be reset after the abnormal condition is cleared, while alarms caused by certain system or cross-check abnormalities may require the power to be turned off. Follow the procedure for the exact CNC, software, machine, and alarm combination rather than relying on repeated resets.
After correcting the confirmed cause:
- Verify that the axis follows correctly through acceleration, full travel, deceleration, and reversal.
- Confirm the intended No.1838/No.1841 selection in both *VLDVx states.
- Confirm No.1828 if it is used as the No.1841 fallback.
- Test the axis under the approved maximum load and motion profile.
- Confirm that SV0475, SV1071, and related safety alarms do not recur.
- Complete reference return and all applicable operating-mode tests.
- Perform and document the required Dual Check Safety acceptance test.
- Return the machine to production only after the complete safety function is validated.
Technical References
- FANUC Series 30i-A Dual Check Safety Operator's Manual, B-64004EN/02, safety position-error monitoring, parameters No.1838 and No.1841, SV0475 alarm, and Dual Check diagnosis
- Applicable FANUC Dual Check Safety Connection Manual for the installed CNC series, software, and machine configuration
- Applicable FANUC CNC parameter manual, servo-amplifier maintenance manual, servo-motor manual, and machine-builder safety documentation
Always use the manual edition that applies to the exact CNC, software, Dual Check Safety option, servo amplifier, motor, detector, axis mechanics, and machine. Safety parameters and signal timing are machine-specific and must not be copied from another installation.
Need Help With FANUC SV0475 Alarm?
REACO CNC provides independent FANUC alarm analysis, servo amplifier testing and repair, motor and feedback-system checks, parameter compatibility support, and replacement-drive supply. Send us the complete alarm screen, affected axis, CNC model and software, servo amplifier and motor models, current No.1838/No.1841/No.1828 values, *VLDVx state, and details of exactly when the alarm occurs.
Browse FANUC servo, spindle, and power drives, visit the FANUC Technical Support Center, or contact REACO CNC for assistance.
Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The effective parameter, recovery procedure, and acceptance test depend on the exact CNC, software, Dual Check Safety configuration, and machine.
