Code 27004: Axis %1, difference safe input %2, NCK %3, drive %4
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical Axis %1, difference safe input %2, NCK %3, drive %4 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 = Axis number %2 = Monitoring input %3 = Interface identifier NCK input %4 = Interface identifier drive input Diagnostics Manual (DAsl), 03/2009 Definitions: A difference has been found on the specified safe input. The state of the specified input signal differed in the two monitoring channels NCK and SIMODRIVE611D during the duration set in $MA_SAFE_MODE_SWITCH_TIME. Monitoring in question (%2): SS/SV = Difference in SGE "Deselection of safe operating stop/Safe velocity" SS = Difference in SGE "Safe operating stop" SV = Difference in SGE "Selection safe velocity" SP = Difference in SGE "Selection safe limit position" SVOVR = Difference in SGEs "Selection SG correction" Interface identifier NCK input (%3): DMP<drv><mod><bit>=<value> <drv> = Drive number of terminal block (1...31) <mod> = Submodule number (1...8) <bit> = Terminal number (1...16) <value> = Value of NCK SGE (0,1) SPL For when the SGE is parameterized at the SPL interface. <io> = Parameterizable system vari able range (01=$A_INSID, 02=$A_INSED) <dword> = System variable double word (1,2) <bit> = Bit number in system variable double word (1...32) <value> = Value of NCK SGE (0,1) Onboard input For when the SGE is parameterized at an onboard input. <bit> = Input number = 01...04 <value> = Value of NCK SGE = 0,1 Interface identifier drive input (%4): DBX<byte><bit>=<value > <byte> = Byte number in axial DB (22, 23, 32, 33) <bit> = Bit number in byte (0...7) <value> = Value of drive SGE (0,1) This alarm can be hidden by setting MD $MN_SAFE_DIAGNOSIS_MASK, bit 0 = 0. Reaction: Alarm display. Remedy: Check settings for safe input signals (NCK I/Os, PLC DB parameters). 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 27004 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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