What the C157 alarm means

Joint torque monitoring detected a collision; the robot stopped immediately to protect itself, the tooling and the environment. 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

  • Real collision with workpiece, fixture or person
  • Collision sensitivity set too low for the application
  • Payload settings wrong so normal torque looks like an impact
  • Mechanical binding in a joint
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. Inspect the tool and surroundings for damage first
  2. Back the robot off the collision point in freedrive or joint mode
  3. Verify payload and mounting settings
  4. Adjust collision sensitivity only after confirming the settings are right
  5. If the alarm fires with no contact, check joint backdrivability and calibration
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 C155 — Protective Stop — Robot Cannot Maintain Position
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 C157 alarm mean?

Joint torque monitoring detected a collision; the robot stopped immediately to protect itself, the tooling and the environment. In field practice it belongs to the motion & path family of faults.

QCan I clear a Universal Robots C157 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.