What the C150 alarm means

The robot detected that a joint is approaching its mechanical/software limit and initiated a protective stop; this is the most frequently seen protective stop in production cells. 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

  • Taught points programmed too close to a joint limit
  • Path blends swinging the joint past the safe margin
  • Wrong TCP/mounting settings making the inverse kinematics pick a bad elbow configuration
  • Mechanical hardstop moved or worn
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. Jog away from the limit in joint mode (toward the safe direction)
  2. Reteach the offending via point with more joint margin
  3. Check TCP configuration and mounting settings
  4. Review blend radii near the limit zone
  5. If the joint limit itself is wrong, verify the mechanical zero 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.

Get a Free Remote Diagnosis See Repair Services

Hotline: +86-20-39029800 · WhatsApp: +86-188-1886-2860

Related Motion & Path alarms

C153 — Protective Stop — Position Deviates from Path C154 — Protective Stop — Position in Singularity C155 — Protective Stop — Robot Cannot Maintain Position 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 C150 alarm mean?

The robot detected that a joint is approaching its mechanical/software limit and initiated a protective stop; this is the most frequently seen protective stop in production cells. In field practice it belongs to the motion & path family of faults.

QCan I clear a Universal Robots C150 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.