Code 20170: [Channel %1: ] Machine data $AC_FIFO invalid
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical [Channel %1: ] Machine data $AC_FIFO invalid 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 Definitions: the structure of the FIFO variable $AC_FIFO 1 - $AC_FIFO10 determined by machine data MD28260 $MC_NUM_AC_FIFO, MD28262 $MC_START_AC_FIFO, MD28264 $MC_LEN_AC_FIFO, MD28266 $MC_MODE_AC_FIFO cannot be stored in the R parameter field defined in MD28050 $MC_MM_NUM_R_PARAM. Reaction: NC Start disable in this channel. Interface signals are set. Alarm display. Remedy: Please inform the authorized perso nnel/service department. Increase the number of the R parameters or reduce the FIFO elements. MD28050 $MC_MM_NUM_R_PARAM = MD28262 $MC_START_AC_FIFO + MD28260 $MC_NUM_AC_FIFO * (MD28264 $MC_LEN_AC_FIFO + 6) Program Continuation: Switch control OFF - ON.
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 20170 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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