What the 34251 alarm means

One phase of the incoming three-phase supply to the drive is missing — the rectifier cannot build a proper DC link. This is one of the faults our repair team handles on ABB IRC5 / OmniCore (RobotWare) systems — the cause is usually identifiable within the first on-site inspection.

Most common causes

  • Blown input fuse on one phase
  • Broken supply cable or terminal
  • Upstream breaker or phase-loss relay tripped
  • Utility supply fault
Field note: the first item on this list is what we find most often on real machines. Check it before you go deeper.

Step-by-step field fix

  1. Measure all three input phases at the cabinet
  2. Replace blown fuses and find why they blew
  3. Tighten input terminals
  4. Check upstream breakers and the facility supply
Safety first: never bypass safety circuits or force contactors closed. If the alarm involves E-stop chains, brakes or drive power, and you are not a trained robot technician, contact a professional — wrong moves here can cost you a robot or an injury.

Still stuck? Get an engineer on the phone — right now

Tell us the alarm code, the robot model and what was happening when the alarm came up. Our engineers run these diagnostics every day, and remote diagnosis by phone or video call is free.

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Related Drive & Power Stage alarms

34316 — Motor Current Error 34200 — Communication with All Drive Units Interrupted 34400 — DC Link Voltage Too High
Other brands: we also keep field-fix libraries for Yaskawa · Universal Robots · Kawasaki and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the ABB 34251 alarm mean?

One phase of the incoming three-phase supply to the drive is missing — the rectifier cannot build a proper DC link. In field practice it belongs to the drive & power stage family of faults.

QCan I clear a ABB 34251 alarm myself?

Sometimes. Work through the step-by-step checks on this page — the first listed cause is what we find most often in the field. If the alarm returns after two attempts, or the fault involves power, brakes or safety circuits, stop and call a qualified robot service engineer.

QHow fast can a Henghuan engineer help?

On-site response in the Pearl River Delta within 30 minutes to 3 hours, across mainland China in 1-3 business days, and worldwide within 2-5 business days. Remote diagnosis by phone/WhatsApp/video is available immediately.

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 ABB documentation or contact us. Henghuan is an independent service provider, not affiliated with or endorsed by ABB.