Sanitized Siemens drive troubleshooting case
Siemens axis jumps or faults immediately: a SINAMICS S120 case
A positioning axis could jump unexpectedly or fault immediately when operation was attempted. The problem was traced in this case to a drive/positioning configuration issue on a Siemens SINAMICS S120 with a CU320-2 DP. You do not need engineering software or a fault code to recognize that an axis is behaving unexpectedly and needs careful diagnosis.
Discuss an Axis or Drive FaultWhat an operator may notice without Siemens software
From the machine side, the problem may look like an axis that jumps when asked to operate, will not move, faults immediately, or cannot complete a positioning move. Those observations are useful even if the HMI does not display a Siemens drive alarm number.
If already visible, record the operator message, what the machine was commanded to do, which axis was involved, and whether the issue began after a configuration or commissioning change. These are clues, not proof that the encoder or motor itself has failed.
What the drive diagnostics showed
The positioning drive objects included HEAD_POSITION and LENGTH_STOP on a SINAMICS S120 / CU320-2 DP system. The investigation involved drive configuration, encoder and position feedback, DDS configuration, and a comparison of online drive information.
A07496: EPOS: Enable not possible
In this case, alarm value (2) indicated that the valid actual-position feedback signal was missing. That diagnostic signal did not, by itself, prove a failed physical encoder.
A07441: encoder adjustment status
A07441 was also present. The absolute encoder adjustment status had changed, and the position offset needed to be saved nonvolatile. This was part of the diagnostic picture, not a claim that it alone caused the axis behavior.
Configuration comparison
The team compared online drive information with the drive configuration and examined DDS and position-feedback settings rather than treating the displayed alarm as a complete diagnosis.
A07496 can have different underlying causes. Its alarm value and the installed drive configuration matter; DDS reconfiguration is not a universal fix for A07496.
What resolved this particular configuration issue
In this confirmed case, the corrective sequence was to load the configuration from the drive to the PG, reconfigure the DDS correctly, and load the corrected configuration back to the drive. The issue was successfully resolved: the axis no longer had the misconfiguration behind the jumping/immediate-fault condition. That allowed further progress toward commissioning and getting the machine into production; it does not establish that production had already resumed.
Case-specific result, not a general procedure: The outcome applies to this drive/positioning configuration issue. Do not copy a configuration, change DDS, or enable an axis based on an alarm code alone. Such work requires a qualified person, the actual machine documentation, site authorization, and appropriate safety controls.
For other machine-stop symptoms, see our Siemens machine-down diagnostic guide. A separate S7-1200 / CM 1243-5 TIA Portal migration case concerns PLC/PROFIBUS project compile errors, not this S120 axis fault.
Need onsite Siemens PLC and drive diagnostics?
West Engineering Systems provides onsite industrial controls troubleshooting and diagnostics. Tell us what the axis does, what the operator display shows, and any drive or controller model and fault code already available. We can discuss whether an onsite diagnostic visit is appropriate; this case does not establish where the original work took place.
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