What the SRVO-004 alarm means

The safety fence circuit is open. Common on older RJ3-era controllers still running in used machines. Our engineers run into this alarm every week on FANUC R-30iA / R-30iB / R-30iB Plus controllers, and a single on-site inspection usually identifies the problem.

Most common causes

  • Fence gate open or interlock switch failure
  • Broken wiring in the fence loop (aged cable on old machines)
  • Jumper missing where fence is not used
Field note: In our repair stats the first cause has the highest hit rate, so confirm it first before digging further.

Step-by-step field fix

  1. Close gates and reset
  2. Test each interlock switch in the loop
  3. On older machines, check for brittle/aged wiring in the fence circuit
  4. If the fence is legitimately unused, fit the correct bypass plug - never random jumpers
Safety first: For FANUC srvo-004, this alarm is the safety circuit itself: jumpering a door switch or forcing a contactor removes the protection entirely - no protective action when something happens, and no defensible account of responsibility. What you can check yourself first is Close gates and reset; the e-stop chain and safety circuit handling is not a DIY job.

How we diagnose safety-chain faults on site

FANUC srvo-004 belongs to the safety chain & e-stop family. On FANUC srvo-004 the failing stage is Dual Check Safety (e-stop board plus dual-channel safety circuit) on the R-30iB Plus / R-30iB Mate Plus / R-30iA - continuity of one series loop: e-stop buttons, door switches, light curtains, safety relays and the enabling device. We start reading FANUC srvo-004 at the iPendant ALARM screen (SRVO / MOTN / SYST / INTF prefixes) together with the amplifier's 7-segment status code.

The chain involved in FANUC srvo-004 runs: e-stop / door / curtain -> safety relay (dual channel) -> controller safety input -> motor-off and brake apply.

FANUC srvo-004 is sometimes designed behaviour, not a fault - Releasing the enabling device (three-position switch) in manual mode triggers a protective stop by design, yet plenty of sites report it as an alarm. The switch enables only in the middle position; fully released or pushed through both open - and pushing through is the instinctive panic reaction, which is exactly what the designers used. Knowing that clears a good share of mysterious protective stops. The real fault is worn contacts inside the switch, showing up as poor contact in the middle position.

Field notes on this page cover FANUC srvo-004 (Fence Open (Legacy RJ3)); written by the Henghuan repair team, updated 2026-10-01.

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Related Safety Chain & E-Stop alarms

SRVO-105 — Door Open or E.Stop SRVO-201 — Panel E-Stop SRVO-202 — TP E-Stop SRVO-204 — External E-Stop (SVEMG Abnormal) SRVO-230 — Chain 1 (+24V) Abnormal SRVO-231 — Chain 2 (0V) Abnormal
Same family: this code belongs to the Safety chain & e-stop alarms family - the page collects all Safety chain & e-stop-family codes we have handled, with the common inspection order and spares.
Other brands: see our KUKA, ABB, Yaskawa and Universal Robots field-fix libraries — or the full 10-brand hub.

Frequently asked questions

QWhat does the FANUC srvo-004 alarm mean?

The safety fence circuit is open. Common on older RJ3-era controllers still running in used machines. Our engineers run into this alarm every week on FANUC R-30iA / R-30iB / R-30iB Plus controllers, and a single on-site inspection usually identifies the problem. FANUC srvo-004 sits in the safety chain & e-stop family; on our work orders the highest-frequency trigger for this code is "Fence gate open or interlock switch failure".

QCan I clear a FANUC srvo-004 alarm myself?

Whether FANUC srvo-004 clears on its own depends on the outcome of "Close gates and reset". Finish the flow with "If the fence is legitimately unused, fit the correct bypass plug - never random jumpers" to confirm FANUC srvo-004 - do not skip it. If that step is clean, the second most frequent cause on FANUC srvo-004 is "Broken wiring in the fence loop (aged cable on old machines)". If FANUC srvo-004 returns after two clears, or the checks point at Fence gate open or interlock switch failure, stop the cell and call a professional robot repair engineer.

QA safety-chain fault like FANUC srvo-004 stops the line - how fast can you be here?

The commonest causes we see on FANUC srvo-004 are "Fence gate open or interlock switch failure, Broken wiring in the fence loop (aged cable on old machines), Jumper missing where fence is not used", so we stock the van against those. For FANUC srvo-004 specifically, we stock along the loop: safety relays, common door switches, e-stop buttons, light-curtain pairs and terminal blocks. For FANUC srvo-004, a safety-chain fault stops the whole line, so we rank it top priority and pre-triage by phone: door switch, e-stop or relay. Before we roll, tell us what FANUC srvo-004 shows on the iPendant ALARM screen (SRVO / MOTN / SYST / INTF prefixes) together with the amplifier's 7-segment status code and what the machine was doing - phone or video triage is free.

This page on FANUC srvo-004 was compiled from actual repair records of the Henghuan Robotics repair team. Alarm notes are our own summary for troubleshooting reference only and may vary with controller and software version — please consult FANUC documentation or contact us if in doubt. Henghuan is an independent service provider, not affiliated with or endorsed by FANUC.