Onsite Siemens drive diagnostics

SINAMICS G120 drive won't start or shows a fault?

A motor that will not run can reflect an active drive fault, a switching-on inhibited state, a missing start command, or a condition elsewhere in the machine. Those are different investigations, not interchangeable diagnoses. West Engineering Systems provides onsite industrial controls troubleshooting to identify the fault and help determine the next action. We are based in Appleton, Wisconsin, and provide field service across the United States.

Discuss Your G120 Drive Problem

Prefer to talk through what the drive displays? Call (920) 851-6363.

Describe what happens before assuming a drive has failed

Fault or alarm is displayed

Record the exact code and message, whether it is active now, and whether it appeared before or after the motor stopped. A displayed fault, an alarm and the machine's HMI message can be different pieces of evidence. Do not assume the last message shown initiated the event.

Ready, but motor does not run

A ready indication is not proof that a start command and usable speed setpoint reached the drive. If the display instead says switching-on inhibited, keep that exact wording; it points to a different status from a drive that is already running. The configured control source and machine sequence matter.

Starts, then trips or stops

Note how far the machine progressed, whether a drive fault appeared, and the time relative to the operator request. A trip under operation calls for a different comparison than a missing start request. The code and installed drive documentation matter more than a guessed fix.

The particular G120 Control Unit, Power Module, firmware and connection to the machine determine which diagnostics are available. Siemens' G120 CU240B-2/CU240E-2 list manual includes fault and alarm information for those Control Units; use documentation applicable to the actual installed model rather than treating one code explanation as universal.

Possible diagnostic areas for a qualified onsite investigation

Start with observations already available on the operator display and the machine history. With authorized access and the applicable project/manual, a controls professional can compare:

  • Drive status and fault history: Is there an active fault, an alarm, or a switching-on inhibited status? Which message or event came first? Keep the exact displayed code and any accompanying value rather than clearing the fault to make the screen blank.
  • Command path and control source: What does the machine request, and where is the G120 configured to receive its start command and speed setpoint? Check the evidence at the PLC/HMI and drive sides before concluding that the motor or drive hardware failed. Siemens' G120 Control Unit operating instructions cover inverter control and switching the motor on and off for specified variants.
  • Enables and safety state: An enable or safety-related condition may prevent torque or start-up. This is a reason for authorized diagnosis, never a reason to bridge an input or defeat a safety function. Siemens provides a separate Safety Integrated manual for the G120 family.
  • Communication and response: If PLC-to-drive communication is part of the installation, compare the requested command, drive status and observed motor response. A missing command, a communication event, a drive trip and a process interlock call for different next steps.

What a diagnostic visit can establish: which available evidence points to a control request, enable, communication or drive-fault area, and what further action is justified. A symptom or code alone does not prove a failed drive, motor, cable, sensor or other component.

What to gather before calling

If already visible or documented, have this information ready:

  • Facility location, machine name and what the motor or machine was supposed to do.
  • Exact drive fault or warning code, active status and any displayed value; photos of the display and corresponding HMI message are useful.
  • Whether the motor never starts, starts then stops, or fails only in a particular existing operating mode. Note the last successful action and approximate time of the first fault.
  • The G120 Control Unit and Power Module model/order numbers, if already known, and whether the issue began after a change or power event. Do not open an enclosure just to get a label.
  • Machine drawings, drive documentation, an unmodified project backup if available, and a contact who can authorize safe diagnostic access.

Is the G120 drive the right place to start?

If the Siemens PLC is in RUN but the whole machine will not begin its sequence, the PLC-in-RUN start-request guide covers the broader machine logic before assuming the G120 received a command. If the source of the machine stop is unknown, start with the Siemens machine-down guide.

An axis that jumps or faults immediately on a SINAMICS S120 is a different motion-control problem. Our S120 positioning-axis case documents a confirmed, case-specific configuration finding; it is not evidence of a fix for a G120 that will not start.

Service scope: We provide onsite troubleshooting, diagnostics and fault identification to help determine next actions. We do not promise a restart, replacement or equipment repair during a visit.

Request onsite Siemens drive diagnostics

Tell us where the machine is, what the G120 and HMI show, and what operation was requested. We can discuss whether an onsite diagnostic visit is a fit.

Request Service

Or call (920) 851-6363 or email info@westengineeringsystems.com.