Code 16943: [Channel %1: ] Action %2<A LNX> not possible due to ASUP
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical [Channel %1: ] Action %2<A LNX> not possible due to ASUP alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
Parameters: %1 = Channel ID %2 = Action number/action name Definitions: The action in the 2nd parameter was rejected, sinc e an asynchronous subprogram is currently active. Currently, only the integrated search run is rejected wi th this alarm. The integrated search run is activated, if search run is triggered in the Stop program state. In other words: Parts of a program have already been executed and a following program part is "skipped" with search run in order to continue the program afterwards. The event is not possible if the program is stopped within an asynchronous subprogram or if an asynchronous subprogram had been selected before the ev ent. An asynchronous subprogram is selected, when the triggering asynchronous subprogram event arrives, but the asynchronous subprogram cannot be started (e.g. the asynchronous start program is not started because of a read-in disable or because the Stop key is active). In this case, it is irrelevant whether a user ASUP or a system ASUP has been triggered. User ASUPs are activated via FC-9 or via the fast inputs. The following events lead to system ASUPS: - Mode change - Overstore on - Canceling subprogram level - Switching on of single block, type 2 - Setting machine data effective - Setting user data effective - Change skip levels - Dry run on/off - Program test off - Correction block alarms - Editing modi in Teach - External zero offset - Axis exchange - Delete distance-to-go - Measuring Reaction: Alarm display. Remedy: Repeat the action after the end of the asynchronous subprogram. Program Continuation: Clear alarm with the Delete key or NC START.
Source: SINUMERIK 840D sl / 840Di sl / SINAMICS S120 Diagnostics Manual (DAsl, 03/2009)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Siemens SINUMERIK 840D CNC Alarms
Siemens controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 16943 on the SINUMERIK 840D CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Siemens's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4014 Siemens SINUMERIK 840D CNC codes.
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