Posted 9 Nov 2017 Hello, As the title indicates, we have a micrologix 1400 that has been installed for a long time. Recently it faulted out on 71h and was in Remote Mode. Do these PLCs revert to Remote Mode when in a fault condition? We placed it back in Run Mode and everything worked fine, but how did it get to Remote Mode in the first place? Thanks, J Share this post Link to post Share on other sites
Posted 9 Nov 2017 Error 71h is" The controller cannot communicate with an expansion I/O module." The controller will stop scanning for safety reasons. You need to find out which module is causing the fault. the xx before the xx71h is the module that is not communicating. If no number then the controller cannot tell. its up to you the find it. error71h.pdf 1 person likes this Share this post Link to post Share on other sites
Posted 9 Nov 2017 The processor was running in Remote-Run before the fault. This allows swapping mode from the software and allows online programming changes. Many programmers will leave the processor in Remote-Run if there is a secure environment. I have never heard of a processor changing from Run to remote, but a major fault will always stop the program unless captured in some sort of fault routine. As Mickey indicated, you will see this again if you have not resolved what caused the fault in the first place. Share this post Link to post Share on other sites
Posted 9 Nov 2017 Thank you for the quick responses. It makes more sense now. The last person that programmed it did leave it in remote-run. Would this fault have automatically reset if it was in Run mode? Or is it always a manual reset type of fault? It hasn't happened again since the reset. Thank you again Share this post Link to post Share on other sites
Posted 9 Nov 2017 No run mode would not have mattered. You can add logic to handle some faults but if you have I/O that is not accessible to the processor then it is a problem that needs to be addressed. Share this post Link to post Share on other sites