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Code 16020: [Channel %1: ] Repositioning in block %2 is not possible

Issue Description & Safety Warning

The Siemens SINUMERIK 840D CNC has triggered a critical [Channel %1: ] Repositioning in block %2 is not possible 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 number %2 = Block number, label Definitions: Programming or operator action incorrect: Repositioning via REPOS command is only possible in an asynchr onous subprogram (interrupt routine). If the REPOS command was programmed, e.g. in the main program or in a cycle, part program execution is aborted with alarm 16020. In addition, the alarm is output in the following situations: - Access to $AC_RETPOINT (repositioning poi nt) outside an ASUP (e.g. in the main program) - An axis to be repositioned was a oscillating axis with sychronous infeed (OSCILL) in the interrupted block and is now in a state that does not allow it to be traversed as a osci llating axis. Remedy: Change the axis to "neutral axis" stat e before repositioning with WAITP. - An axis to be repositioned was an infeed axis for a os cillating axis in the interrupted block; now it can no longer be traversed as one. Remedy: Change the ax is back to "POS axis" state before repositioning. Reaction: Interpreter stop NC Start disable in this channel. Interface signals are set. Alarm display. Remedy: Modify the part program if necessary. Program Continuation: Clear alarm with the RESET key. Restart part program

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 16020 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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