Posted 19 Aug 2019 (edited) Has anyone had an issue with Siemens plc's occasionally going out of run mode? I was doing some research and found that it could be due to a bad analog input. Is there a way to tell which input or output is causing this fault? I know I can create a hardware diagnostics error organization block but that only correct from what I've read. Edit: I've added a screen shot of the diagnostics report. The fault that may be the problem is: Temporary CPU error: Serious firmware exception CPU changes to DEFECTIVE mode (system reaction) This plc / system was installed 2 year ago and we've had this problem occasionally since. I'm guessing the wrong firmware was used during the install. Will try upgrading firmware this weekend. Edited 19 Aug 2019 by ihatemitsubishiplcs added information Share this post Link to post Share on other sites
Posted 19 Aug 2019 Go online and look in the diagnostic buffer what cpu? 1 person likes this Share this post Link to post Share on other sites
Posted 19 Aug 2019 Would this show past faults even if the CPU was put back into run mode? It was a co worker who put the plc back into run mode and I'm just trying to find out why it keeps happening. Also the PLC is an IM 155-6 PN ST Thanks for your help. Share this post Link to post Share on other sites