Siemens SINUMERIK Alarm 25000 — Drive Fault Fix

Error Code: Siemens SINUMERIK Alarm 25000

What it means: Alarm 25000 (and the broader 25xxx alarm range) on Siemens SINUMERIK 828D and 840D sl CNC controllers indicates an axis drive fault — a problem detected by the CNC in its interface with the SINAMICS S120 servo drive system. The alarm number within the 25xxx range identifies the specific axis and fault type: for example, Alarm 25001 typically means “drive fault on axis 1,” while 25050 indicates a communication fault between the NCU (numerical control unit) and the drive.

SINUMERIK alarms in this range are extremely common on 828D/840D machines in the field because they cover the entire drive-to-control interface — hardware, firmware, parameter, and communication faults all fall under this category.

Common Causes

• SINAMICS S120 drive internal fault — The drive module (Motor Module or Power Module in the S120 booksize/chassis format) has detected an internal hardware fault, overcurrent, overvoltage, or overtemperature condition. The drive’s own fault code appears on the SINAMICS operator panel (BOP-2) or in Starter/TIA Portal.
• Drive-CNC communication failure (DRIVE-CLiQ) — The DRIVE-CLiQ fiber optic or copper communication link between the NCU and the SINAMICS drive components has experienced a fault. A disconnected, damaged, or incorrectly routed DRIVE-CLiQ cable produces alarm 25000.
• Encoder feedback fault — The absolute encoder (SMx encoder module) has lost communication or is returning implausible values. Common after encoder battery replacement or after machine relocation.
• Motor overtemperature — The motor’s KTY84 or PT100 temperature sensor has detected a thermal alarm from the motor windings or bearing area.
• DC link undervoltage — The S120 power supply module (Active Line Module or Basic Line Module) is not providing adequate DC bus voltage. Caused by utility voltage dip, line module fault, or blown line fuse.
• Parameter incompatibility after drive replacement — After a drive module replacement, if the drive’s parameter set doesn’t match the machine tool builder’s configuration, alarm 25000 appears on first power-up.

Step-by-Step Fix {#step-by-step-fix}

1. Read the full alarm text on the SINUMERIK operator panel. Alarms display in the Alarm menu (accessible via the Alarm key or the Info softkey). The 25xxx alarm text includes the axis name and a sub-text that describes the specific fault type. Write down the complete alarm text — “Axis X1: Drive fault 25201” tells you far more than just “25000.”

2. Read the SINAMICS drive fault on the drive itself. Navigate to the SINAMICS S120 drive unit (in the electrical cabinet). If equipped with a BOP-2 panel (Basic Operator Panel), press the Alarm/Fault button to read the SINAMICS fault number. Common SINAMICS faults that correspond to SINUMERIK 25xxx alarms: F7900 (internal fault), F30001 (overcurrent), F30002 (overvoltage), F30003 (undervoltage), F30004 (overtemperature), F31130 (encoder fault). Record the exact SINAMICS fault number.

3. Check DRIVE-CLiQ connections. DRIVE-CLiQ is the daisy-chain communication bus that connects the NCU to the Line Module, Motor Modules, SMx encoder modules, and other S120 components. Inspect each DRIVE-CLiQ connector (the distinctive green square connectors with a latch clip) for secure seating. A single loose DRIVE-CLiQ connector can generate a cascade of 25xxx alarms across multiple axes.

4. Check the Line Module status LED. The Active Line Module (or Smart Line Module) has status LEDs on its front face. Green = OK. Red = fault. Yellow = pre-warning. A red LED on the Line Module means DC bus power is not being provided correctly — check input fuses, input contactor, and line voltage at the Line Module input terminals.

5. Verify encoder connection and battery (for absolute encoders). SMx encoder modules equipped with a battery-backed absolute encoder (common on 840D machines) will fault after battery replacement until the encoder is re-referenced. Navigate to the machine datum menu and perform a machine zero return (reference point approach) for the affected axis.

6. Review the SINAMICS parameter backup. If the 25xxx alarm appeared after a drive module swap, the drive needs its parameters downloaded from the machine’s parameter backup. On 828D, the parameter backup is stored on the CF card. On 840D, it’s stored on the PCU-50 or directly on the NCU. Use SINUMERIK Operate or Siemens Starter software to download the correct parameter set to the replacement module.

7. Check motor cooling. If the SINAMICS fault is F30004 (overtemperature), check that the motor’s built-in cooling fan is running (liquid-cooled motors have a coolant flow check). Confirm the motor’s KTY or PT100 sensor cable is connected at the Motor Module’s X21 or X25 connector.

8. Clear alarms and test. After addressing the root cause, navigate to the SINUMERIK Alarm menu and select “Acknowledge All” or press the Reset button. If alarms are persistent (require power cycle to clear), cycle power to the entire machine (NCU, drives, and PLC) in sequence: drives off first, then NCU, then back on in reverse order.

Parts That May Need Replacement {#parts-that-may-need-replacement}

When to Call a Professional

SINUMERIK 828D/840D systems require Siemens-trained technicians for drive replacement and parameter commissioning. Incorrectly loaded parameters can cause axis runaway, position reference loss, or damage to the machine’s mechanical components. Siemens provides remote support via TeleService for 828D/840D systems — your machine tool dealer can often initiate a remote session where a Siemens engineer reads the drive diagnostic data directly via the network and identifies the root cause without a site visit. Always maintain a current parameter backup on removable media and store it with the machine documentation.

Pro tip: SINUMERIK 25xxx alarms triggered by DRIVE-CLiQ communication issues often correlate with a specific time of day — typically early morning when the facility’s HVAC first kicks on and creates vibration. A DRIVE-CLiQ cable that has a marginal connection will intermittently break continuity with vibration. Wiggle each DRIVE-CLiQ cable gently while watching the alarm screen — if an alarm clears or appears when you disturb a specific cable, you’ve found it.