# How to troubleshoot the following error- Fault Robotinterface : C4A17: Communication issue: Communication with joint 5 lost

**URL:** <https://forum.universal-robots.com/t/how-to-troubleshoot-the-following-error-fault-robotinterface-c4a17-communication-issue-communication-with-joint-5-lost/36200>\
**Category:** Robot Communication\
**Created:** [September 25, 2024, 3:58am UTC](https://forum.universal-robots.com/t/how-to-troubleshoot-the-following-error-fault-robotinterface-c4a17-communication-issue-communication-with-joint-5-lost/36200 "2024-09-25T03:58:45Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![andre.kyme](https://avatars.discourse-cdn.com/v4/letter/a/7993a0/32.png) [@andre.kyme](https://forum.universal-robots.com/u/andre.kyme)\
**Post date:** [September 25, 2024, 3:58am UTC](https://forum.universal-robots.com/t/how-to-troubleshoot-the-following-error-fault-robotinterface-c4a17-communication-issue-communication-with-joint-5-lost/36200/1 "2024-09-25T03:58:45Z")

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We have started to encounter problems initialising our UR3 (it hangs during power up). It appears to be related ti the following error:  
_Fault_  
_Robotinterface : C4A17: Communication issue: Communication with joint 5 lost._  
We have followed the limited advice in the “C4 Communications Issue” part of the manual - which is to check all the comms lines and to reboot. The problem seems to be deeper than this. Can anyone advise who has had a similar/same error?

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**Author:** ![efn](https://avatars.discourse-cdn.com/v4/letter/e/35a633/32.png) [@efn](https://forum.universal-robots.com/u/efn)\
**Post date:** [September 25, 2024, 6:27am UTC](https://forum.universal-robots.com/t/how-to-troubleshoot-the-following-error-fault-robotinterface-c4a17-communication-issue-communication-with-joint-5-lost/36200/2 "2024-09-25T06:27:35Z")

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It sounds like a faulty joint to me, if the error happens during initializing. I haven’t encountered that error before, where it could be fixed by anything other than a new joint.

What part of the initialization does it happen at? Power On or Brake Release? 🙂

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**Author:** ![andre.kyme](https://avatars.discourse-cdn.com/v4/letter/a/7993a0/32.png) [@andre.kyme](https://forum.universal-robots.com/u/andre.kyme)\
**Post date:** [September 25, 2024, 11:49am UTC](https://forum.universal-robots.com/t/how-to-troubleshoot-the-following-error-fault-robotinterface-c4a17-communication-issue-communication-with-joint-5-lost/36200/3 "2024-09-25T11:49:04Z")

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Thanks - the problem happens during initialisation. The initialsiation hangs and there is no sound of the brakes releasing.

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**Author:** ![efn](https://avatars.discourse-cdn.com/v4/letter/e/35a633/32.png) [@efn](https://forum.universal-robots.com/u/efn)\
**Post date:** [September 25, 2024, 11:55am UTC](https://forum.universal-robots.com/t/how-to-troubleshoot-the-following-error-fault-robotinterface-c4a17-communication-issue-communication-with-joint-5-lost/36200/4 "2024-09-25T11:55:37Z")

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I don’t think there’s much to do besides contact your local distributor. They should be able to offer a repair of the current joint (cheaper, but takes longer and more work) or a new joint.