FANUC SV0474 means that the servo processor detected a stopped-axis position deviation greater than the limit specified by parameter No.1839 or No.1842. This alarm belongs to the position-error monitoring function of FANUC Dual Check Safety. The alarm message may appear as SV0474 EXCESS ERROR (STOP:SV), with the affected axis identified on the CNC screen.
| Alarm item | Meaning |
|---|---|
| CNC alarm | SV0474 EXCESS ERROR (STOP:SV) |
| Detection side | Servo CPU / servo DSP |
| Detection state | The axis is judged to be stopped |
| Monitored value | Servo following error, also called position deviation |
| Applicable limit | No.1839 when safety monitoring is requested; No.1842 when it is not requested |
| Official first check | Confirm that No.1839 and No.1842 are correctly set and not unnecessarily small |
| Safety response | Alarm output and an immediate stop equivalent to an emergency stop on applicable systems |
For a wider alarm-number reference, see the FANUC SV Alarm Codes guide.
What Does FANUC SV0474 Mean?
A FANUC servo system compares the commanded axis position with position feedback from the motor pulse coder or the configured position detector. The difference is the position deviation, following error, or servo error. A small deviation can remain even after a movement command has ended because the servo loop is still holding the commanded position.
Dual Check Safety independently monitors this deviation in the CNC CPU and the servo CPU. SV0474 is generated when the servo side determines that the absolute stopped-state position deviation has exceeded the applicable safety limit.
This alarm identifies the monitored condition, but it does not by itself identify one failed component. A limit that is too small can generate SV0474 even when the axis behaves normally. The same alarm can also reveal a genuine inability to hold position, an axis that has not settled before the stopped-state check becomes active, a brake or mechanical problem, a feedback abnormality, unsuitable servo data, or an unexpected external load.
Do not treat SV0474 as an ordinary machining-tolerance message. The monitored value is servo following error, not the finished-part dimensional error. The alarm is part of a safety function and can remove machine drive power through the safety sequence.
How No.1839 and No.1842 Are Selected
The effective parameter depends on the state of the Dual Check Safety monitoring request signal *VLDVx for the affected axis:
| Dual Check Safety state | Signal state | Stopped-state limit | Meaning |
|---|---|---|---|
| Safety monitoring is being carried out | *VLDVx = 0 | No.1839 | Stopped-axis position-deviation limit during safety monitoring |
| Safety monitoring is not being carried out | *VLDVx = 1 | No.1842 | Stopped-axis position-deviation limit outside the active safety-monitoring state |
No.1839 and No.1842 are axis-type, two-word parameters specified in the detector unit on the systems covered by the cited Dual Check Safety manual. The documented setting range is 0 to 99,999,999, but the correct value is machine-specific. It depends on detector resolution, servo behavior, mechanical design, holding requirements, safety design, and the machine builder's risk assessment.
There is one important exception: when No.1842 is set to 0, the cited manual states that No.1829 is used as the stopped-state limit while *VLDVx is 1. When *VLDVx is 0, No.1839 remains the applicable safety-check limit.
| Condition when SV0474 occurs | Parameter to verify first |
|---|---|
| Alarm occurs after the safety-monitoring request becomes active | No.1839 and the *VLDVx transition timing |
| Alarm occurs while the safety-monitoring request is inactive | No.1842 |
| No.1842 is 0 | No.1829, because it becomes the fallback stopped-state limit |
| Signal state is uncertain | Use the Dual Check diagnosis and machine ladder documentation before editing any parameter |
Changing both values without identifying the signal state can hide the diagnostic evidence and alter a safety-related threshold unnecessarily.
Do Not Simply Increase the Deviation Limit
The official check mentions values that may be too small, but that does not mean the proper repair is always to increase No.1839 or No.1842. A larger limit permits more axis displacement before the safety function reacts. If the deviation is caused by a slipping brake, gravity-loaded axis, mechanical movement, feedback fault, or incorrect sequence, increasing the limit can conceal a hazardous condition.
Before changing either parameter:
- Back up the complete CNC, servo, PMC, and Dual Check Safety configuration.
- Record the original value for every affected axis.
- Confirm which parameter is active from the *VLDVx state.
- Measure or record the actual position deviation at the alarm event.
- Compare the active data with the machine builder's verified backup and safety documentation.
- Confirm that the proposed value preserves the machine's risk-reduction requirements.
- Follow the required password, authorization, power-cycle, checksum, and acceptance-test procedure.
The cited manual indicates that a power-off operation is required before operation can continue after these safety-parameter settings are changed. Any modification must therefore be treated as a controlled safety-system change, not an alarm-reset shortcut.
Safety Before Troubleshooting
SV0474 can occur because an axis is physically moving or drifting when it should be stopped. Before entering the machine or working near an axis, isolate hazardous energy and support any vertical, inclined, suspended, counterbalanced, or gravity-loaded component. Do not assume that a stopped command means the mechanism cannot move.
Do not bypass *VLDVx, force a safety input, defeat the brake, change ladder logic, or widen the deviation limit merely to keep the machine running. Parameter editing, powered tests, brake tests, and Dual Check Safety validation must be performed by qualified personnel under the applicable FANUC and machine-builder procedures.
1. Confirm the Exact Alarm, Axis, and Detection Side
Record the alarm before resetting or switching off the CNC:
- The complete message SV0474 EXCESS ERROR (STOP:SV)
- The affected axis and machine position
- Whether SV1072 or another Dual Check Safety alarm appears at the same time
- The CNC series, model, software, and Dual Check Safety option
- Servo amplifier, motor, detector, and brake specifications
- Whether the alarm occurs at power-up, after reference return, after deceleration, when a guard or safety state changes, or after an emergency-stop sequence
- Recent parameter restoration, motor or amplifier replacement, feedback work, brake work, ladder modification, or mechanical repair
The suffix STOP:SV is significant. It distinguishes servo-side stopped-position monitoring from CNC-side monitoring and from moving-state or servo-off monitoring. Diagnose the complete number shown rather than grouping every excess-error alarm together.
2. Determine Exactly When the Position Deviation Increases
Observe the position-deviation diagnostic value using the procedure approved for the installed CNC and machine. The useful question is not only whether the value exceeded the limit, but how it reached the limit.
Determine whether the deviation:
- Is already high before the axis is declared stopped
- Decays normally after deceleration but the safety state changes too early
- Rises slowly while the axis should be holding position
- Jumps when a brake, clamp, hydraulic circuit, or counterbalance changes state
- Appears only at one physical position
- Occurs only under a heavy fixture, workpiece, head, or rotary-table load
- Oscillates with vibration or audible hunting
- Changes after the cabinet warms up or after a cable moves
If the deviation is genuinely increasing at standstill, preserve that evidence. Increasing No.1839 or No.1842 would change when the alarm occurs but would not correct the loss of position control.
3. Verify No.1839, No.1842, and the No.1829 Fallback
Compare the active parameter values with the verified machine backup and the applicable FANUC parameter manual. Do not copy settings from a different machine, even when the CNC and motor models appear similar.
Check the following:
- Confirm that the affected axis has the intended No.1839 value.
- Confirm that No.1842 has the intended value for operation while safety monitoring is not requested.
- If No.1842 is 0, verify the effective fallback value in No.1829.
- Confirm that the units are detector units and that the configured detector resolution has not changed.
- Review any recent parameter restore, servo initialization, CNC memory replacement, option change, motor replacement, or detector change.
- Confirm that values have not been copied between axes with different mechanics, resolutions, brakes, or loads.
An unexpectedly small value may be the direct reason that normal settling deviation crosses the threshold. An unexpectedly large value is also a safety concern and should not be accepted simply because it prevents the alarm.
4. Check the Dual Check Safety Request Timing
The technician-supplied advice to check the trigger timing is relevant because the selected stopped-state limit changes with *VLDVx. Review the machine ladder, safety design, and Dual Check diagnostic information to determine when the signal changes and whether the axis has reached a stable stopped condition at that moment.
Check for:
- A safety-monitoring request that becomes active before deceleration and servo settling are complete
- A brake or clamp command that changes state before the servo has safely transferred the load
- A mode, guard, door, or emergency-stop transition that changes *VLDVx unexpectedly
- Chattering or intermittent safety input wiring
- A ladder, safety-I/O, or commissioning change that altered the intended sequence
- A mismatch between the machine builder's documented sequence and the active PMC logic
Correcting timing does not mean deliberately delaying or defeating a required safety response. The signal sequence must match the validated machine safety design. If a sequence change is necessary, it requires authorization, risk assessment, verification, and the prescribed acceptance test.
5. Check for Actual Axis Drift at Standstill
If the active parameter and signal timing are correct, determine whether the mechanism is moving when it should remain stationary. This is especially important for vertical axes, inclined axes, robot-like mechanisms, rotary tables, tool heads, and axes with counterbalance systems.
Inspect for:
- A holding brake that slips, drags, releases too early, or applies too late
- Incorrect brake-coil voltage, damaged brake wiring, or an abnormal brake air gap
- Low hydraulic or pneumatic pressure in a counterbalance or clamp circuit
- Internal leakage in a hydraulic balancing cylinder
- Mechanical backlash, a loose coupling, damaged key, slipping belt, or loose pulley
- Ballscrew, gearbox, bearing, or guideway damage
- External force from tooling, process pressure, a fixture, or an unbalanced load
- A collision or obstruction that prevents the commanded position from settling
Use physical position checks, load data, brake feedback, pressure readings, and servo diagnostics as specified by the machine builder. Never release a brake or disconnect a counterbalance on an unsupported gravity-loaded axis.
6. Inspect Servo Feedback and Holding Performance
SV0474 is not a dedicated pulse-coder disconnection alarm, but incorrect or unstable feedback can make the servo processor calculate an abnormal stopped-position deviation. Give the feedback system priority when there are simultaneous detector alarms, erratic position values, recent motor or encoder work, or a fault that changes when a cable moves.
With power safely isolated, inspect:
- Pulse-coder or scale connectors for looseness, contamination, bent pins, or damaged locks
- Feedback-cable continuity, shielding, grounding, routing, and flex damage
- Separation of low-level feedback wiring from motor, contactor, and other high-power cables
- Correct motor, detector, and axis assignment after maintenance
- Detector mounting and coupling integrity
- Motor and amplifier compatibility and all model suffixes
Also check whether the servo can produce stable holding torque. Motor-power wiring, a missing phase, poor terminal contact, an intermittent winding, unsuitable servo data, amplifier output problems, excessive load, or unstable gain can prevent the axis from holding within the expected deviation.
Do not replace the pulse coder, motor, or amplifier based on SV0474 alone. Use simultaneous alarms, waveform or diagnostic data, continuity checks, substitution with exact compatible components, and machine history to identify the defective item.
7. Review Servo Parameters and Recent Initialization
Incorrect motor identification, detector resolution, flexible-feed-gear data, direction, loop gain, load inertia, brake timing, or machine-specific servo values can affect the stopped-state deviation. Compare the complete active data with a verified backup for the exact machine.
Reinitializing servo parameters is justified only when data was lost, corrupted, or loaded incorrectly. It is not a routine reset for SV0474. Initialization can overwrite machine-builder adjustments and safety-related values. If it is required, save the current data, use the exact motor and detector information, restore the machine-specific settings, and complete commissioning and safety validation.
If the alarm began immediately after data restoration, identify every changed value rather than adjusting No.1839 or No.1842 in isolation.
8. Use the Dual Check Diagnosis Screen
On applicable FANUC systems, the Dual Check diagnosis screen can display the state of safety-related signals and the cause of a safety alarm. The cited operator's manual describes reaching this screen from the SYSTEM function by displaying the DUAL CHECK soft key.
Use the screen together with the ladder and electrical drawings to record:
- The safety-monitoring request state for the affected axis
- The alarm source and detection side
- Related safety inputs and outputs
- Whether the CNC and servo checks report corresponding conditions
- The state immediately before and after the alarm
Screen names and access steps vary by CNC series and software. Do not alter safety data from a diagnostic screen unless the applicable manual and authorized procedure specifically require it.
9. Understand the Paired CNC-Side Alarm
Dual Check Safety monitors the same safety-relevant behavior through independent paths. For stopped-state position deviation, the relevant pair is:
| Detection side | Alarm | Meaning |
|---|---|---|
| Servo CPU / servo DSP | SV0474 | Servo-side stopped-position deviation exceeded No.1839 or No.1842 |
| CNC CPU | SV1072 | CNC-side stopped-position deviation exceeded No.1839 or No.1842 |
If both alarms are present, record both. One should not be casually dismissed as a duplicate because the independent detection paths are part of the Dual Check Safety architecture. If only one appears, diagnose the exact detection side and review the applicable manual rather than replacing hardware by assumption.
Difference Between SV0474 and Related Excess-Error Alarms
| Alarm | Detection side | Axis state | Applicable limit on the cited system |
|---|---|---|---|
| SV0474 | Servo CPU | Stopped | No.1839 or No.1842 |
| SV1072 | CNC CPU | Stopped | No.1839 or No.1842 |
| SV0475 | Servo CPU | Moving | No.1838 or No.1841 |
| SV1071 | CNC CPU | Moving | No.1838 or No.1841 |
| SV1070 | Servo CPU | Servo off | No.1840 |
| SV1069 | CNC CPU | Servo off | No.1840 |
SV0474 should also not be confused with an ordinary stopped-position deviation alarm outside the Dual Check Safety context. Confirm the exact CNC series, option, alarm text, and manual because parameter use and recovery procedures can vary.
FANUC SV0474 Diagnostic Table
| Finding | Interpretation | Recommended action |
|---|---|---|
| No.1839 or No.1842 differs from the verified machine backup | Safety deviation data may have been changed, lost, or restored incorrectly | Preserve the current data, identify the effective parameter, and restore only through the authorized safety procedure |
| No.1842 is 0 | No.1829 is the effective stopped-state limit while *VLDVx is 1 | Verify No.1829 before assuming that a zero value disables monitoring |
| Alarm occurs exactly when *VLDVx changes | Axis settling and safety-request timing may not match | Review the validated ladder sequence, stopped-state timing, and actual deviation trace |
| Deviation slowly increases while stopped | Axis may be drifting or losing holding torque | Secure the mechanism; inspect brake, counterbalance, load, mechanics, motor power, and amplifier output |
| Alarm occurs on a vertical axis as the brake changes state | Brake or load-transfer timing may be abnormal | Follow the builder's supported-axis and brake test procedure; do not bypass the brake |
| Alarm changes when a feedback cable moves | Cable, connector, shielding, or detector connection may be intermittent | Isolate power and inspect or test the feedback circuit |
| Alarm began after servo initialization or parameter restore | Motor, detector, gain, or safety data may not match the machine | Compare the entire servo and DCS configuration with a verified backup |
| SV0474 and SV1072 appear together | Both independent monitoring paths detected excessive stopped deviation | Record both and diagnose the actual deviation, effective limit, and sequence |
| Values and sequence are correct but the axis hunts at stop | Servo instability, mechanical looseness, or feedback noise may be present | Diagnose with servo waveform and mechanical evidence before adjusting gain |
| External conditions and configuration are verified | Servo amplifier control or feedback processing may be faulty | Professionally test or replace the exact compatible unit, then perform full safety validation |
Recommended Troubleshooting Order
- Record the complete SV0474 message, affected axis, alarm history, operating state, and any simultaneous alarms.
- Secure the mechanism, especially a gravity-loaded or suspended axis, before entering the hazard area.
- Determine whether the alarm occurs at power-up, after motion stops, during a brake or clamp transition, or when a safety state changes.
- Record the actual position-deviation behavior instead of immediately increasing a limit.
- Check the *VLDVx state to identify whether No.1839 or No.1842 is active.
- If No.1842 is 0, verify the fallback stopped-state limit in No.1829.
- Compare the active settings with the verified backup and the exact machine's safety documentation.
- Review the timing of the safety-monitoring request, brake, clamp, and state-transition logic.
- Inspect the axis for genuine drift, brake slip, counterbalance problems, excessive load, looseness, or mechanical movement.
- Inspect feedback and motor-power circuits when the diagnostics, maintenance history, or simultaneous alarms support that direction.
- Compare motor, detector, servo, and safety parameters with the verified machine data; initialize only when justified.
- Use the Dual Check diagnosis screen to preserve signal-state and alarm-source evidence.
- Test the servo amplifier only after configuration, sequence, mechanics, brake, load, and external wiring have been checked.
- Make any safety-parameter or sequence change only through the approved change-control and risk-assessment procedure.
- After repair, complete the required power-cycle, reference-return, functional test, and Dual Check Safety acceptance test before returning the machine to production.
Reset and Post-Repair Verification
Do not rely on repeated resets to clear SV0474. Depending on the CNC series, software, safety state, and test mode, recovery may require removal of the cause, a controlled reset, a power cycle, or another procedure specified by FANUC and the machine builder.
After correcting the confirmed cause:
- Verify that the axis settles and holds position under all intended loads.
- Confirm the brake, clamp, counterbalance, and safety-state sequences.
- Confirm that the correct stopped-state limit is selected in both *VLDVx states.
- Check that SV0474, SV1072, and related safety alarms do not recur.
- Test reference return and all applicable operating modes.
- Perform the required Dual Check Safety acceptance test and document the results.
- Restore production only after the machine's complete safety function has been validated.
Technical References
- FANUC Series 30i-A Dual Check Safety Operator's Manual, B-64004EN/02, position-error monitoring, SV0474 alarm, parameters No.1839 and No.1842, 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 signals are machine-specific and must not be copied from another installation.
Need Help With FANUC SV0474 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.1839/No.1842/No.1829 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.
