Sinamics G120 P0010 Reverts to 1 After Power Cycle: Fix

1. Problem Definition

The Sinamics G120 control unit (CU230P-2, CU240B-2, CU240E-2, CU250S-2, and variants) forces parameter P0010 back to the value 1 each time the three-phase line supply is removed and re-applied. With P0010 = 1 the drive sits in Quick Commissioning mode and refuses the ON command, so the motor cannot start until the operator manually re-enters P0010 = 0. The symptom is reported across firmware releases 4.4 through 5.2 and across all BOP-2, IOP-2, and STARTER/TIA Portal commissioning paths.

Typical field observations that accompany this fault:

• Drive will not run after a power outage or after an intentional main-supply disconnect.
• P0010 reads 1 on every power-up although the operator previously set it to 0.
• Other commissioning parameters (motor nameplate data, ramp times, control source) also revert to factory or last-saved values.
• The Basic Operator Panel (BOP-2) or Intelligent Operator Panel (IOP-2) intermittently displays NO CONN while the drive continues to run from terminal commands.
• The BOP-2 alternates between the parameter number P0010 and the value 1 without operator input.

2. Root Cause Analysis

Sinamics G120 parameters are held in two physically separate memory areas. The interaction between them is the root cause of the reported symptom.

When a parameter is changed through the BOP-2, IOP-2, or any commissioning tool, the new value is written to RAM only. The drive uses the RAM copy during operation. On the next power-on cycle the control unit copies the ROM contents back into RAM. If the RAM change was never copied to ROM, it is overwritten and lost.

The mechanism that produces the specific P0010 = 1 symptom is the commissioning filter. Quick Commissioning is the default state on the first power-up of a new or factory-reset Control Unit, so the installer can step through the basic motor and application parameters. The control unit stays in P0010 = 1 only if the user does not execute the End of quick commissioning sequence: setting P0010 = 0 and then triggering a save.

Three distinct failure paths lead to the symptom:

1. Save step omitted. The user changed P0010 from 1 to 0 in RAM only and never executed P0971 = 1. The non-volatile copy still holds P0010 = 1, so every power cycle reloads it.
2. Save step executed but interrupted. The user triggered P0971 = 1 and removed power before the write to EEPROM completed (3-45 s on most control units). The partial write is discarded and the old P0010 = 1 value remains in ROM.
3. Parameter filter conflict. The user set P0010 = 0 while P0003 = 2 (extended access) was still active and a follow-on parameter write re-entered P0010 = 1 through an OEM tool or PLC function block.

Field evidence from multiple installations also shows the symptom appears when the operator uses the BOP-2 quick-number entry mode (P followed by the parameter number), which does not always display the success or failure of the save action. The IOP-2 with its graphical interface makes the save state visible through the status bar icon.

3. P0010 Parameter Reference

P0010 selects the parameter filter for commissioning. It does not control the drive; it controls which other parameters can be modified at the current access level. The values are standardized across the Sinamics G110, G120, G120C, G120D, G120P, and G150 families.

While P0010 is in any non-zero value the drive will not accept an ON command. The status word bit 1 (ZSW1.1 in r0052) reflects drive not ready. Some control unit firmware versions will also issue warning A0351 Drive commissioning not yet complete or A0352 No power section available for the configured configuration if the drive is left in P0010 = 1.

4. P0971 Save Parameter Reference

P0971 is the explicit save-to-non-volatile-memory command. Unlike most Sinamics parameters, P0971 is a write-only parameter; its value is not stored - it triggers an action and then resets to 0 automatically.

During the save the control unit's RDY (Ready) LED is steady green, the BF (Bus Fault) LED is off, and the SF (Safety Fault) LED is off. Do not remove power, do not pull the control unit from the power module, and do not reset the drive while the save is in progress. Interrupting the save can corrupt the EEPROM, forcing a factory reset and full re-commissioning.

For G120 firmware versions 4.7 SP3 and later, parameter r3996 reports the save status:

If the BOP-2 or IOP-2 shows the save failed, the EEPROM may be near end-of-life (typical endurance 1,000,000 write cycles per cell) or there may have been an undervoltage condition during the write. Replace the control unit if the failure repeats.

5. Step-by-Step Resolution Procedure

Apply the following sequence to clear the persistent P0010 = 1 state. The procedure assumes a control unit that is otherwise healthy and is reachable from the operator panel.

5.1 Prerequisites

• Control Unit catalog number (e.g. 6SL3244-0BB12-1BA1 for CU240B-2, 6SL3244-0BB13-1BA1 for CU240E-2).
• Current firmware version, readable from r0018.
• BOP-2 (6SL3255-0AA00-4BA1) or IOP-2 (6SL3255-0AA00-4JA1) with the cable inserted fully into the control unit.
• Access level P0003 = 3 (expert) to see commissioning parameters.

5.2 Using the BOP-2

1. Apply 24 V or three-phase line voltage to the drive. Wait for the BOP-2 to show the actual frequency (0.00 Hz) or the parameter number.
2. Press the P key, then enter 10 and press P again. BOP-2 displays the current value of P0010.
3. If the value is 1, confirm. Press the up/down keys to change to 0 and press P to accept. The display briefly shows busy and then returns to the parameter number.
4. Press P, enter 971, press P. The BOP-2 shows 0.
5. Press the up key once to change the value to 1 and press P. The BOP-2 shows a flashing busy and the RDY LED stays solid green for 3-45 s.
6. Wait for the BOP-2 to return to the parameter display. Do not remove power. If busy persists longer than 60 s, cycle the 24 V supply (the main supply can stay on) and re-enter P0971 = 1.
7. Once the BOP-2 shows the parameter number P0971 and the value 0, the save is complete.

5.3 Using the IOP-2

1. From the IOP-2 home screen, open Menu > Parameters > Commissioning filter.
2. Set P0010 = 0 and confirm with the OK button.
3. Open Menu > Parameters > Save to memory card / Non-volatile. The IOP-2 displays Save RAM to ROM.
4. Tap Save. A progress bar appears; the save takes 5-60 s.
5. The IOP-2 displays Save complete when finished.

5.4 Using STARTER or TIA Portal

1. Connect the commissioning PC to the control unit via PROFINET, PROFIBUS, or the mini-USB service port (CU240E-2 and CU250S-2 only).
2. Open the project, go online with the drive, and load the drive into the project if not already present.
3. In the parameter list, navigate to P0010 and set it to 0. Click Download to drive.
4. Right-click the drive in the project tree and select Copy RAM to ROM. STARTER / TIA Portal writes the entire RAM image to the non-volatile memory and reports Save successful in the message log.
5. Optionally use the Save to memory card action to mirror the parameters to a SIMATIC CF card or SD card for backup.

6. BOP-2 / IOP-2 "NO CONN" Issue

The NO CONN message on the BOP-2 or IOP-2 is a related but distinct symptom that often appears in the same fault report. It means the control unit's operator-panel interface has not established a logical connection with the panel.

6.1 Hardware Causes

• BOP-2 cable not fully seated in the control unit's RS-232 socket.
• Damaged cable or kinked cable (especially at the strain relief).
• Foreign material on the connector pins (oil, dust, flux residue).
• Defective panel electronics (BOP-2 catalog 6SL3255-0AA00-4BA1 is field-replaceable).
• Control Unit RS-232 transceiver damaged by electrostatic discharge or by a hot-plug event while the control unit was powered.

6.2 Software / Configuration Causes

• Control unit firmware older than 4.3 does not support the BOP-2 in all parameter sets; upgrade to the latest firmware available for the catalog number.
• Communication protocol on the operator-port interface has been redirected (parameter P2018 set to a non-default value).
• Two operator panels connected simultaneously (BOP-2 plus IOP-2 plus mini-USB). The interface supports only one logical panel at a time.

6.3 Diagnostic Steps

1. Power the control unit down and back up. The NO CONN message is normal for the first 1-2 s after power-on; it should clear once the RDY LED turns green.
2. Disconnect the BOP-2, inspect the connector for bent pins, and reconnect firmly until the latch clicks.
3. Try a known-good BOP-2 from a spare drive.
4. Read r2050 and r2051 (USS / Modbus diagnostic counters) - any incrementing value indicates a working serial link to the panel.
5. If the message persists across multiple BOP-2 units, replace the control unit.

The fact that the drive continues to run from terminal commands while the BOP-2 shows NO CONN confirms the drive logic is healthy and the issue is on the operator-panel link only. This is not related to the P0010 save issue and can be addressed in parallel.

7. Verification Procedure

After applying the resolution, verify the fix with the following sequence. Each step has a specific pass criterion.

1. Read-back of P0010 on the BOP-2. With the drive powered, navigate to P0010 on the BOP-2. The value must read 0. Press P to exit without changing.
2. Power-cycle test. Remove the three-phase line supply. Wait 30 s for the DC bus to discharge below 50 V (verify with a meter on the DC+ and DC- terminals). Re-apply the line supply.
3. Read-back of P0010 after power-up. Repeat step 1. The value must still read 0. If it reads 1, the save did not commit - go back to Section 5.
4. Run command acceptance. With the BOP-2 showing 0.00 Hz, press the green I (Run) key. The drive should accelerate to the setpoint at the configured ramp rate. Press the red O (Stop) key. The drive should ramp down to zero at the configured OFF ramp.
5. Status word check. Read r0052 (ZSW1). Bit 0 must be 1 (drive ready) and bit 1 must be 0 (no fault active) for the drive to accept a run command.
6. Save status check. Read r3996 on firmware 4.7 SP3 and later. The value must be 0 (save complete).

If the drive passes all six checks, the issue is resolved. Record the firmware version, parameter snapshot, and date in the drive's maintenance log.

8. Best Practices for Parameter Persistence

Apply the following practices on every Sinamics G120 commissioning job to prevent recurrence of the P0010 reversion symptom and similar RAM-only changes.

• Always end quick commissioning with a save. After setting P0010 = 0, execute P0971 = 1 before disconnecting the commissioning PC or powering down the drive.
• Use STARTER or TIA Portal for batch changes. Single-parameter changes through the BOP-2 are easy to forget to save. PC-based tools force a final "Copy RAM to ROM" step before disconnecting.
• Adopt the P3900 shortcut for quick commissioning. Setting P3900 = 1, 2, or 3 at the end of quick commissioning automatically calculates the motor data, sets P0010 = 0, and performs a non-volatile save. This is the recommended path on firmware 4.4 and later.
• Document the save status in the commissioning report. Record the value of r3996 immediately after the save to prove the write completed.
• Avoid P0010 = 1 during normal operation. If a parameter edit is required during production, change the parameter value directly and save with P0971 = 1. Do not toggle P0010 as a write-enable workaround unless the parameter is in the quick-commissioning set.
• Use a CF or SD card as a backup medium. After the final save, copy the parameter set to a SIMATIC memory card. This allows a complete restore if the control unit is replaced.

9. Related Parameters and Edge Cases

Several other Sinamics G120 parameters interact with the P0010 / P0971 save behavior. Engineers debugging similar symptoms should check the following.

Edge case: on a G120 with PM330 power module and firmware 5.1 SP1, a power-down shorter than 5 s can leave the control unit in a state where the RAM image is preserved by the internal supercapacitor but the ROM copy is marked invalid. On the next power-up the drive reverts to the previous ROM copy. Allow a minimum 10 s power-down for a clean reset.

10. Troubleshooting Matrix

The following matrix maps common field symptoms to root cause and resolution. Use it as a triage guide when the symptom description is brief.

11. References and Standards

The parameter numbering, commissioning sequence, and save behavior described in this article are documented in the official Siemens Sinamics G120 operating instructions and parameter (list) manual. Engineers should consult the manual for the exact control unit catalog number to confirm version-specific behavior.

• Siemens Industry Online Support - search for "Sinamics G120" to access the current operating instructions, parameter list manual, and firmware release notes for every control unit variant.
• Sinamics G120 product support - manuals and firmware - direct entry point for the G120 product family manuals, including the operating instructions for the CU230P-2, CU240B-2, CU240E-2, and CU250S-2 control units.
• Sinamics G120 firmware download portal - access the latest firmware releases, release notes, and HSP (Hardware Support Package) files for STARTER and TIA Portal.