What the C155 alarm means

With servos on, the robot drifts or cannot hold its position; the controller suspects an incorrectly configured payload and stops. This is one of the faults our repair team handles on Universal Robots CB3 / e-Series (UR5/UR10/UR16/UR20) systems — the cause is usually identifiable within the first on-site inspection.

Most common causes

  • Payload mass or center of gravity set wrong
  • Gripper/tool weight changed (empty vs full) without updating the payload
  • Brake wear on a heavily loaded axis
  • Mounting orientation configured incorrectly
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. Re-measure the real tool weight and center of gravity
  2. Update the payload in the active installation
  3. Use payload switching programs if the tool grips parts
  4. Test brake holding by enabling servos at the affected pose
  5. Replace worn brakes if drift persists with correct payload
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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Hotline: +86-20-39029800 · WhatsApp: +86-188-1886-2860

Related Motion & Path alarms

C150 — Protective Stop — Position Close to Joint Limits C153 — Protective Stop — Position Deviates from Path C154 — Protective Stop — Position in Singularity C157 — Protective Stop — Collision Detected
Other brands: we also keep field-fix libraries for Kawasaki · Staubli · Epson and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the Universal Robots C155 alarm mean?

With servos on, the robot drifts or cannot hold its position; the controller suspects an incorrectly configured payload and stops. In field practice it belongs to the motion & path family of faults.

QCan I clear a Universal Robots C155 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 Universal Robots documentation or contact us. Henghuan is an independent service provider, not affiliated with or endorsed by Universal Robots.