Lenze 940 Servo Drive Fault Codes List 2026 – Troubleshoot your Lenze 940 servo drive with our updated 2026 fault code guide. Learn to read error logs via L-force Engineer, interpret status LEDs, and reset major trips.
The Lenze 9400 series (often referred to as the 940 Servo) is a high-performance drive used in precision motion control. When the drive trips, it communicates its status through a series of hexadecimal error codes or via the status LEDs on the front faceplate.
This guide provides the most updated resources for 2026 to help you interpret these fault codes, utilize Lenze’s diagnostic software, and minimize downtime in your production line.
Lenze 940 Fault Codes Reference Table
Below is the reference for the Lenze 9400/940 series protective functions. Please refer to your existing list to match the code on your display or software with the specific diagnostic remedy.
| Fault Code and Meaning | Cause and Remedy |
|---|---|
| F_OU Over voltage | Cause: Drive bus voltage reached the maximum level, typically due to motor regeneration. Remedy: Check deceleration time or install a braking resistor. |
| F_FB Feedback error | Cause: Invalid Hall sensors code; Resolver signal lost or at least one motor hall sensor is inoperable or not connected. Remedy: Check encoder/resolver wiring and Hall sensor connections. |
| F_OC Over current | Cause: Drive exceeded peak current limit. Software incapable of regulating current within 15% for more than 20mS. Remedy: Check for wrong motor data, poor tuning, or short circuit in motor cables. |
| F_Ot Over temperature | Cause: Drive heatsink temperature has reached maximum rating (100°C or 108°C depending on model). Remedy: Check ambient temperature, cooling fans, and cabinet ventilation. |
| F_OS Over speed | Cause: Motor has reached velocity above its specified limit. Remedy: Check speed loop tuning and commanded velocity limits. |
| F_PE Position Error Excess | Cause: Position error has exceeded maximum allowed value. Remedy: Check for mechanical jams, motor sizing, or increase position error tolerance. |
| F_bd Bad motor data | Cause: Motor profile data is invalid or no motor is selected. Remedy: Verify motor parameters in the configuration software. |
| F_EP EPM failure | Cause: EPM (Electronic Programming Module) failure on power up. Remedy: Replace the EPM module or try re-seating it. |
| -EP- EPM missing | Cause: EPM not recognized (connected) on power up. Remedy: Ensure the EPM is properly inserted into the slot. |
| F_09 Motor over temperature | Cause: Motor over temperature switch activated or PTC indicates motor windings reached maximum temperature. Remedy: Allow motor to cool; check motor load and cooling. |
| F_10 Subprocessor failure | Cause: Error in data exchange between processors. Usually occurs when EMI level is high. Remedy: Check for poor shielding and grounding of the system. |
| F_14 Under voltage | Cause: Bus voltage level drops below 50% of nominal bus voltage while operating. Remedy: Check incoming AC line voltage and power supply stability. |
| F_15 Hardware overload protection | Cause: Phase current becomes higher than 400% of total drive current capability for more than 5μs. Remedy: Check for short circuits or extreme mechanical overload. |
| F_18 Arithmetic Error / Division by zero | Cause: Statement executed within Indexer Program results in division by zero. Remedy: Check and correct the drive source code logic. |
| F_19 Arithmetic Error / Register overflow | Cause: Indexer Program generated a value too large for the requested register. Remedy: Review variable types and math operations in the program. |
| F_20 Subroutine stack overflow | Cause: Exceeded 32 levels of subroutine stack depth (excessive calls without RETURN). Remedy: Verify program logic to ensure all calls have corresponding RETURN statements. |
| F_25 Unknown opcode | Cause: Byte code interpreter error; missing END statement or corrupted EPM data. Remedy: Re-download the program or replace the EPM. |
| F_27 Drive disabled | Cause: Attempt to execute motion while the drive is disabled. Remedy: Enable the drive before commanding motion in the program. |
| F_32 Positive Limit Switch | Cause: Positive limit switch is activated. Remedy: Move the axis in the negative direction or check the switch wiring. |
| F_36 Drive Disabled by User at Enable Input | Cause: Drive is disabled during operation or attempt to enable without deactivating “Inhibit”. Remedy: Check the state of the hardware Enable and Inhibit inputs. |
| F_45 2nd Encoder Position Error | Cause: Second encoder position error has exceeded maximum value. Remedy: Check the secondary encoder alignment and wiring. |
How to Read Lenze 940 Faults via L-force Engineer
While the physical LEDs provide a basic status, connecting your PC to the drive using the Lenze L-force Engineer (or Global Drive Control – GDC for legacy models) software provides the most accurate diagnostic data for 2026 maintenance standards.
- Logbook: Access the “Logbook” to view the chronologically ordered history of all warnings and faults. Each entry includes a timestamp and an “Occurrence” count.
- Sub-Codes: Pay close attention to the sub-codes in the diagnostic menu. These identify whether a fault like “Overcurrent” is happening in the motor cable, the power section, or due to a short circuit to earth.
- Oscilloscope Function: L-force Engineer allows you to trace current and speed values. This is essential for diagnosing intermittent OC1 or OU trips that occur only during specific parts of the motion cycle.
General Troubleshooting Steps
Before performing a manual reset on your Lenze servo system, perform these essential hardware checks:
- Verify Resolver/Encoder Connection: Servo drives are highly sensitive to feedback signals. Ensure resolver cables are shielded and that the shield is properly grounded at the drive.
- Check the DC Bus: For OU (Overvoltage) trips, verify the external braking resistor. Use a multimeter to check the resistance value against the drive’s specifications.
- Thermal Inspection: If the drive trips on OH (Overheat), ensure the internal fan is spinning and that there is sufficient clearance in the electrical cabinet for airflow.
Frequently Asked Questions (FAQ)
Q: What is the difference between a Warning and a Trouble?
A: A Warning (indicated by a flashing LED or ‘W’ prefix) alerts you that a limit is being reached (e.g., motor temperature), but the drive stays active. A Trouble or Fault (indicated by a solid red LED or ‘F’ prefix) disables the power stage and stops the motor immediately.
Q: How do I reset a Lenze 940 fault?
A: Once the cause is resolved, you can reset the drive by:
- Using the Reset command in the L-force Engineer software.
- Activating the digital input assigned to the “Trip Reset” function.
- Cycling the 24V control power. Note: Major hardware faults may require a full mains power cycle.
Q: What does the LED status “Ready” vs “Inhibit” mean?
A: Ready means the drive is healthy and waiting for a start signal. Inhibit (or Controller Inhibit) means the drive is technically healthy, but the “Enable” signal (typically terminal 28 or X5/DI4) is missing, preventing the motor from turning.
Q: Where is the fault history stored in the parameters?
A: You can find the fault history in the Diagnostic (D) group. Parameters like C00168 often store the current fault, and the history log can be accessed via the keypad menu under “Diagnostics.”