Code 230903: <location>Power unit: I2C bus error occurred
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>Power unit: I2C bus error occurred 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
Message value: %1 Drive object: All objects Reaction: A_INFEED: NONE (OFF1, OFF2) SERVO: NONE (IASC/DCBRAKE, OFF1, OFF2, OFF3, STOP1, STOP2) VECTOR: NONE (IASC/DCBRAKE, OFF1, OFF2, OFF3, STOP1, STOP2) Acknowledge: IMMEDIATELY Cause: Communications error with an EEPROM or A/D converter. Fault value (r0949, interpret hexadecimal): 80000000 hex: - internal software error. 00000001 hex... 0000FFFF hex: - module fault. Remedy: Re fault value = 80000000 hex: - upgrade firmware to later version. Re fault value = 00000001 hex... 0000FFFF hex: - replace the module.
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 230903 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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