Siemens Micromaster F0071 — What It Means
F0071 on a Siemens Micromaster 420 or 440 drive is a USS setpoint communication fault. The drive is configured to receive its speed or process setpoint over the USS serial link, but that data stream has stopped arriving for longer than the permitted telegram timeout window. In plain terms, the drive is waiting for valid setpoint data from a PLC, HMI, BOP-link, or other USS master controller and the communication partner is no longer sending it.
This is a communication protocol fault, not a motor power, overload, or overcurrent fault. The drive cannot operate because it has no valid speed command. The fault clears once communication resumes and the drive receives a reset command.
Common Causes
- Master device not transmitting The PLC, HMI, or USS master controller is powered off, faulted, or not running the communication program correctly.
- Broken or loose communication wiring The serial cable between the drive and master has a broken conductor, loose terminal connection, or failed shield ground.
- Incorrect USS parameter setup The drive and master have mismatched communication settings for link selection, baud rate, telegram format, or timeout values.
- Communication board or interface failure An add-on communications card or BOP-link interface module in the drive has failed or unseated from its connector.
- Wrong control source selected The drive is configured to expect USS setpoint input but the application actually uses a different control method such as analog input or keypad.
Step-by-Step Fix
- Verify the active control source by reviewing the drive parameters on the keypad or BOP to confirm the drive is set to receive setpoint commands over the USS link and not from another source.
- Check the master device to confirm the PLC, HMI, or USS controller is powered on, running its program, and actively transmitting valid setpoint telegrams to the drive.
- Inspect the communication cable and terminals between the drive and master for loose connections, broken wires, damaged insulation, or missing shield ground connections at both ends.
- Review and match communication parameters on both the drive and master side including USS link selection, baud rate, node address, telegram timeout settings, and data format to eliminate configuration mismatches.
- Check the communication board or interface if the drive uses an add-on card by powering down the drive, reseating the board in its slot, and inspecting for damage or loose connectors.
- Clear the fault after restoring communication by cycling drive power, pressing the reset button on the keypad or BOP, or activating the configured digital input reset signal.
- Swap in known-good components such as a spare communication cable, interface module, or test master device to isolate whether the fault is on the drive side, master side, or wiring side if the fault returns.
Parts Often Needed
| Part | Notes |
|---|---|
| USS communication cable (RS-485 or RS-232) | Amazon | Match connector type and pinout to your Micromaster model and master device interface. |
| Siemens communication board or interface module | Amazon | Order the correct card for your drive frame size and protocol if the onboard interface has failed. |
| BOP-link connector or adapter | Amazon | Replacement connector hardware if the physical BOP or USS link interface is damaged. |
When to Call a Pro
Call a qualified controls technician or automation specialist if you have verified the master device is running and the wiring is intact but the fault persists, or if you are not familiar with USS protocol parameter setup and telegram troubleshooting. Professional help is also appropriate if the drive requires a replacement communication board or if the fault is part of a larger system integration issue involving multiple networked drives or a complex PLC program. Do not attempt communication board replacement or advanced parameter changes without training on Siemens Micromaster drives and the specific master controller in your application.