What the 4105 alarm means

The EMERGENCY connector loop check failed — the controller cannot verify the external emergency stop circuit. Our engineers run into this alarm every week on Epson RC90 / RC700 (EPSON RC+) controllers, and a single on-site inspection usually identifies the problem.

Most common causes

  • EMERGENCY connector not plugged or not latched
  • E-stop wiring open or shorted
  • External E-stop device failed
  • Connector pin damage
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. Check that the EMERGENCY connector is fully seated and latched
  2. Inspect the E-stop loop wiring for opens and shorts
  3. Test each external E-stop device
  4. Repair or replace the connector if pins are damaged
  5. Reboot the controller after the loop is healthy
Safety first: For EPSON 4105, 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. On site you may look at after confirming power-off the first step yourself: Check that the EMERGENCY connector is fully seated and latched. Beyond that it is the e-stop chain and safety circuit work - leave it to a professional.

How we diagnose safety-chain faults on site

EPSON 4105 belongs to the safety chain & e-stop family. On EPSON 4105 the failing stage is safety circuit plus safety-function options on the RC700-A / RC90-B and the RC series - continuity of one series loop: e-stop buttons, door switches, light curtains, safety relays and the enabling device. We start reading EPSON 4105 at the EPSON RC+ error list and controller front-panel indicators; codes segment as 4xxx / 5xxx / 9xxx.

The chain involved in EPSON 4105 runs: e-stop / door / curtain -> safety relay (dual channel) -> controller safety input -> motor-off and brake apply.

EPSON 4105 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 EPSON 4105 (Emergency Connector Connection Failure); written by the Henghuan repair team, updated 2026-10-01.

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Related Safety Chain & E-Stop alarms

4150 — Redundant Input Signal Failure of Emergency Stop
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: we also keep field-fix libraries for Nachi · Omron · ESTUN and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the EPSON 4105 alarm mean?

The EMERGENCY connector loop check failed — the controller cannot verify the external emergency stop circuit. Our engineers run into this alarm every week on Epson RC90 / RC700 (EPSON RC+) controllers, and a single on-site inspection usually identifies the problem. EPSON 4105 sits in the safety chain & e-stop family; on our work orders the highest-frequency trigger for this code is "EMERGENCY connector not plugged or not latched".

QCan I clear a EPSON 4105 alarm myself?

Whether EPSON 4105 clears on its own depends on the outcome of "Check that the EMERGENCY connector is fully seated and latched". Finish the flow with "Reboot the controller after the loop is healthy" to confirm EPSON 4105 - do not skip it. If that step is clean, the second most frequent cause on EPSON 4105 is "E-stop wiring open or shorted". Two attempts and still there means stop: EPSON 4105 involves the e-stop chain and safety circuit, and running EPSON 4105 on can turn a repairable fault into a replacement.

QA safety-chain fault like EPSON 4105 stops the line - how fast can you be here?

The commonest causes we see on EPSON 4105 are "EMERGENCY connector not plugged or not latched, E-stop wiring open or shorted, External E-stop device failed", so we stock the van against those. For EPSON 4105 specifically, we stock along the loop: safety relays, common door switches, e-stop buttons, light-curtain pairs and terminal blocks. For EPSON 4105, 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 EPSON 4105 shows on the EPSON RC+ error list and controller front-panel indicators; codes segment as 4xxx / 5xxx / 9xxx and what the machine was doing - phone or video triage is free.

This page on EPSON 4105 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 Epson documentation or contact us. Henghuan is an independent service provider, not affiliated with or endorsed by Epson.