Siemens Drive Fault Code 7902 Site

If using an encoder, incorrect wiring or scaling can cause the drive to think the motor is not moving. Step-by-Step Troubleshooting Guide Follow these steps to diagnose and clear the 7902 fault. Step 1: Check the Mechanical System

typically indicates a "Drive: Communication board (CB) link error" or a loss of communication via the PROFINET/PROFIBUS interface.

Program longer acceleration ramps ( p1120 ) for heavy loads to allow torque to build up gradually. If you need help adjusting these settings, let me know: The exact Siemens drive model (e.g., G120, S120) Whether you use an encoder or run in sensorless control The type of mechanical load connected to the motor Share public link

Regrease bearings if the motor utilizes reloadable grease nipples. 3. Locate the Maintenance Parameters siemens drive fault code 7902

| Root Cause | Solution | |------------|----------| | PLC in STOP | Set PLC to RUN or reconfigure drive to ignore missing telegram ( p2040 = 0 – not recommended for safety) | | p2040 too short | Increase p2040 to at least 2–3× bus cycle time | | Loose connector | Reseat or replace bus connector | | Wrong telegram type | Match p0922 with PLC configuration (e.g., standard telegram 1 for speed control) | | No termination | Activate termination on both ends of PROFIBUS segment | | EMI | Check cable routing, add ferrites, verify shield grounded at both ends | | Faulty option board | Replace communication board (e.g., CBE20 for PROFINET) |

Option 1: Quick Troubleshooting (Best for LinkedIn/Professional Forums)

Check for mechanical obstructions (brake locked, jammed load). Check motor cable connectivity. If using an encoder, incorrect wiring or scaling

Increase the low-speed voltage boost parameters ( to p1312 ) if using U/f control to inject extra torque at startup.

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A loose connection or failing contactor in the output side. Program longer acceleration ramps ( p1120 ) for

Alternatively, increase the interval limit in if your operational schedule allows for longer intervals between servicing.

Siemens SINAMICS drives, including the popular G120XA and G120 series, are known for their robustness. However, motor control faults can occur, with being a common issue in both high-inertia applications and malfunctioning systems.

In technical terms, the drive’s internal motor model compares the expected motor speed (based on the setpoint) against the actual speed feedback (or an estimated value). If the deviation between what should be happening and what is happening exceeds a predefined threshold for a set amount of time, the drive shuts down and raises the F7902 fault to prevent damage to the mechanics, the motor, or the drive itself.

The drive's parameters do not match the actual motor (e.g., rated current, power factor, or resistance). Incomplete Identification:

When a Siemens drive encounters code F07902, the inside the firmware has flagged a critical discrepancy. The drive's internal calculator compares the expected speed model against either actual encoder feedback or its internal encoderless calculation matrix. If the motor is running at full torque or current limit and its speed drops significantly below the setpoint for longer than a specified delay time, the drive shuts down via an OFF2 (coast to stop) command to protect the motor from burning out. F07900 vs. F07902: What is the Difference?