What the SRVO-348 alarm means

The Dual Check Safety (DCS) system detected that the main contactor (MCC) opened abnormally or its feedback does not match the commanded state. This fault appears in a large share of our FANUC R-30iA / R-30iB / R-30iB Plus service tickets, and the first round of on-site checks usually finds the source.

Most common causes

  • MCC contactor failure (welded or burnt contacts)
  • Contactor drive circuit fault
  • Feedback wiring fault
  • DCS parameter/configuration issue after parts replacement
Field note: Most of the time the problem is the first item on the list, so ruling it out saves you half the time.

Step-by-step field fix

  1. Check the contactor and its auxiliary feedback contacts
  2. Verify the contactor drive signal from the E-stop/DCS board
  3. After replacing hardware, verify DCS settings and apply DCS code
  4. Never force the contactor closed to run production
Safety first: For FANUC srvo-348, 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. The self-serviceable action is Check the contactor and its auxiliary feedback contacts; anything past that falls under the e-stop chain and safety circuit and needs a certified engineer.

How we diagnose safety-chain faults on site

FANUC srvo-348 belongs to the safety chain & e-stop family. On FANUC srvo-348 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-348 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-348 runs: e-stop / door / curtain -> safety relay (dual channel) -> controller safety input -> motor-off and brake apply.

On FANUC srvo-348 (field clue usually MCC contactor failure (welded or burnt contacts)) we have one hard rule: On this family we have a hard rule: no bypassing the safety loop, no forcing contactors closed, ever. Some sites jumper the door switch to keep running - that removes the entire protection function, and when something happens there is no protective action and no defensible account of responsibility. We have seen a crush injury caused by exactly that jumper, so we would rather wait for parts than do it. If a customer has already jumpered it, we restore the circuit first and then diagnose the real fault.

Field notes on this page cover FANUC srvo-348 (DCS MCC OFF Alarm); 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-348 alarm mean?

The Dual Check Safety (DCS) system detected that the main contactor (MCC) opened abnormally or its feedback does not match the commanded state. This fault appears in a large share of our FANUC R-30iA / R-30iB / R-30iB Plus service tickets, and the first round of on-site checks usually finds the source. FANUC srvo-348 sits in the safety chain & e-stop family; on our work orders the highest-frequency trigger for this code is "MCC contactor failure (welded or burnt contacts)".

QCan I clear a FANUC srvo-348 alarm myself?

Whether FANUC srvo-348 clears on its own depends on the outcome of "Check the contactor and its auxiliary feedback contacts". Finish the flow with "Never force the contactor closed to run production" to confirm FANUC srvo-348 - do not skip it. If that step is clean, the second most frequent cause on FANUC srvo-348 is "Contactor drive circuit fault". When FANUC srvo-348 keeps coming back it is not a one-off trigger - especially if Never force the contactor closed to run production is where you get stuck. Do not keep producing through FANUC srvo-348.

QA safety-chain fault like FANUC srvo-348 stops the line - how fast can you be here?

The commonest causes we see on FANUC srvo-348 are "MCC contactor failure (welded or burnt contacts), Contactor drive circuit fault, Feedback wiring fault", so we stock the van against those. For FANUC srvo-348 specifically, we stock along the loop: safety relays, common door switches, e-stop buttons, light-curtain pairs and terminal blocks. For FANUC srvo-348, 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-348 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-348 was written by the Henghuan Robotics repair team from field service experience. Alarm descriptions are our own summary for troubleshooting reference and may vary by controller and software version — when in doubt, check your FANUC documentation or contact us. Henghuan is an independent service provider, not affiliated with or endorsed by FANUC.