Code 232123: <location>Encoder 2: Signal le vel A/B unipolar outside tolerance
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>Encoder 2: Signal le vel A/B unipolar outside tolerance 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: Fault cause: %1 bin Drive object: All objects Reaction: A_INFEED: NONE SERVO: OFF1 (IASC/DCBRAKE, NONE, OFF2, OFF3) VECTOR: OFF1 (IASC/DCBRAKE, NONE, OFF2, OFF3) Acknowledge: IMMEDIATELY SINAMICS-Alarms Diagnostics Manual (DAsl), 03/2009 Cause: The unipolar level (AP/AN or BP/BN) for enc oder 2 is outside the permissible tolerance. Fault value (r0949, interpret binary): Bit 0 = 1: Either AP or AN outside the tolerance. Bit 16 = 1: Either BP or BN outside the tolerance. The unipolar nominal signal level of the encoder must lie in the range 2500 mV +/- 500 mV. The response thresholds are < 1700 mV and > 3300 mV. Note: The signal level is not evaluated unless the following conditions are satisfied: - Sensor Module properties available (r0459.31 = 1). - Monitoring active (p0437.31 = 1). Remedy: - make sure that the encoder cables and shie lding are installed in an EMC-compliant manner. - check the plug connections and contacts. - check the short-circuit of a signal cable with mass or the operating voltage. - replace the encoder cable.
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 232123 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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