# Siemens Enhanced Driver CPU 1515F-2PN SYMBOLIC vs ABSOLUTE instability **URL:** \ **Category:** Ignition\ **Tags:** siemens\ **Created:** [May 13, 2026, 7:49am UTC](https://forum.inductiveautomation.com/t/siemens-enhanced-driver-cpu-1515f-2pn-symbolic-vs-absolute-instability/115503 "2026-05-13T07:49:52Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![milton.stathakis](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/milton.stathakis/32/73561_2.png) [@milton.stathakis](https://forum.inductiveautomation.com/u/milton.stathakis)\ **Post date:** [May 13, 2026, 7:49am UTC](https://forum.inductiveautomation.com/t/siemens-enhanced-driver-cpu-1515f-2pn-symbolic-vs-absolute-instability/115503/1 "2026-05-13T07:49:52Z")
Hi everyone, I am currently on Gateway version 8.3.6 Stable and Siemens Enhanced Driver 1.3.6. My connection with a CPU 1515F-2PN was working completely fine with Symbolic addressing until yesterday. Now the connection keeps showing connected/connecting intermittently and bad communication status on tags within designer. When I changed the addressing mode from Symbolic to Absolute that connection became stable once again. This seems to be a replicable bug, and I have changed nothing within the PLC itself since it was working. Is this a known issue? Cheers, Milton ---
**Author:** ![milton.stathakis](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/milton.stathakis/32/73561_2.png) [@milton.stathakis](https://forum.inductiveautomation.com/u/milton.stathakis)\ **Post date:** [May 13, 2026, 8:30am UTC](https://forum.inductiveautomation.com/t/siemens-enhanced-driver-cpu-1515f-2pn-symbolic-vs-absolute-instability/115503/2 "2026-05-13T08:30:17Z")
Update\*\* I have duplicated the exact same SYMBOLIC connection in the Gateway (identical settings). One of these connections now has a stable 'connected' status, the other will continue to drop out. Same port, same address etc. When I delete the duplicate that is dropping out, the stable connection then becomes unstable again. This is also repeatable. ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [May 13, 2026, 11:18am UTC](https://forum.inductiveautomation.com/t/siemens-enhanced-driver-cpu-1515f-2pn-symbolic-vs-absolute-instability/115503/3 "2026-05-13T11:18:24Z")
Sounds like a bug worth reporting to support. (Via the IA Help Center.) ---
**Author:** ![Cody\_Morgan](https://avatars.discourse-cdn.com/v4/letter/c/db5fbb/32.png) [@Cody\_Morgan](https://forum.inductiveautomation.com/u/Cody_Morgan)\ **Post date:** [May 13, 2026, 2:42pm UTC](https://forum.inductiveautomation.com/t/siemens-enhanced-driver-cpu-1515f-2pn-symbolic-vs-absolute-instability/115503/4 "2026-05-13T14:42:14Z")
What firmware version is the PLC? Did you add tags to the symbolic connection before it started going intermittently bad? Are you reading the same tags on the duplicate connection? Try turning on the debug level logs for all of the the siemens symbolic loggers while troubleshooting. This sounds like it could be a known issue with the Siemens firmware, but would need more info to confirm. ---
**Author:** ![Cody\_Morgan](https://avatars.discourse-cdn.com/v4/letter/c/db5fbb/32.png) [@Cody\_Morgan](https://forum.inductiveautomation.com/u/Cody_Morgan)\ **Post date:** [May 13, 2026, 4:00pm UTC](https://forum.inductiveautomation.com/t/siemens-enhanced-driver-cpu-1515f-2pn-symbolic-vs-absolute-instability/115503/5 "2026-05-13T16:00:27Z")
Additional info- the S7-1500 firmware versions that are affected are 4.0.0 through 4.1.0. v4.0.0 is the worst offender, some fixes were made that address most of the problem in v4.0.4. The last I heard from our library vendor, the recommendation was to downgrade to 3.9.x firmware. However, 4.1.2 or 4.1.4 might fix the issue. There is promising information in the release notes for those versions, and the recommendation for 3.9.x was before 4.1.2 was released. If you turn your siemens loggers to debug level, you should see a "connection lost" message in there somewhere, if you're hitting this firmware bug. ---
**Author:** ![milton.stathakis](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/milton.stathakis/32/73561_2.png) [@milton.stathakis](https://forum.inductiveautomation.com/u/milton.stathakis)\ **Post date:** [May 14, 2026, 7:42am UTC](https://forum.inductiveautomation.com/t/siemens-enhanced-driver-cpu-1515f-2pn-symbolic-vs-absolute-instability/115503/6 "2026-05-14T07:42:17Z")
Thanks for the response Cody. I will get that info and post it here when I can get access again. I switched to an OPC UA server on the PLC and client connection in Ignition Gateway and that worked perfectly.