Resolving PROFIdrive SubIndex Error on Siemens G120 CU240E-2

Problem Overview

SINAMICS G120 drives equipped with a CU240E-2 PN Control Unit occasionally reject parameter downloads executed by StartDrive V16 Update 3 with a PROFIdrive error whose text reads "SubIndex invalid". The first failure usually names a BICO list parameter, most commonly p9462[22] ("List of the parameters for BICO signal source"). After a Control Unit reset, the same alarm reappears but points at a different sub-index on subsequent attempts, producing an apparently random pattern of failed parameters on each new download. The alarm persists even though the same values were previously accepted by the drive. The root cause is almost never a defect on the indexed parameter itself - it is a sequencing conflict between the StartDrive download state machine and the SINAMICS operating state.

This technical reference walks through the diagnostic logic, the affected firmware versions, the meaning of p9462, the role of the drive operating state, and a deterministic procedure to clear the alarm and complete the download.

Affected Hardware and Software

The combination of a free telegram with a BICO-heavy commissioning dataset - where p9462[] is rebuilt during the write - tends to expose the SubIndex error. Drive firmware V4.7 SP13 SP2 and the matching Support Package contain the changes that tightened the sub-index handshake. Older HSP releases and HSP-less TIA Portal configurations are more vulnerable to the symptom.

Root Cause Analysis

Every PROFIdrive parameter has the structure (ParameterNumber, SubIndex). The SINAMICS drive exposes multi-element arrays (for example p9462[0..30]) by mapping each element to a unique sub-index of the same parameter number. When the StartDrive download service opens a parameter request it sends the parameter handle first, then opens each sub-index in turn. Three distinct mechanisms trigger a "SubIndex invalid" reply:

1. Drive not in parameter-write state. The SINAMICS state machine distinguishes Commissioning, Ready, Run, Identification, Fault, and Identification. Indexed writes triggered while the drive is in the Commissioning state (the orange "Quick commissioning" prompt) are rejected for any parameter whose sub-index has not yet been built in the firmware. The reply is the generic SUBINDEX_NOT_SUPPORTED alarm.
2. Length mismatch between StartDrive index view and drive index view. When the offline project uses V4.7.13 with a different BICO list count than the connected drive (for example V4.7 SP13 SP2 with extra BICO interconnect objects), the request asks for sub-indices the device has not yet allocated. Each request triggers the same generic reply - which is why the parameter number appears to "move" between attempts.
3. BICO interconnections re-built during download. p9462[] ("List of the parameters for BICO signal source") is rebuilt the moment a BICO source/target pair is committed to the drive. If the StartDrive sequencer commits BICO sources before the sub-index table is refreshed, the freshly added index returns SUBINDEX_INVALID until the next download cycle restarts.

The field insight is that the rotating parameter number is misleading: the underlying fault is the drive state at the moment of the write, not the parameter itself. Once the drive has transitioned to Ready (ZSW1 bit 0 = 1, no bits in the "Commissioning" group), the same parameter set downloads cleanly on the next pass.

What p9462 Means in the SINAMICS BICO Model

Parameter p9462 is the BICO signal source list - the registry of all source-side parameters currently bound to a sink parameter via a BICO interconnection. Each element of p9462[] stores the parameter number, the sub-index and the bit number of one source. Typical contents on a fan application include:

During a full download StartDrive rewrites the entire BICO source list. Each write opens a new sub-index and asks the firmware for the current value of p9462[n] before sending the new entry. The handshake fails when the firmware temporarily cannot answer because the table is mid-rebuild, which then surfaces as SUBINDEX_INVALID.

Do not delete or "blank" p9462 from the project to bypass the alarm. The list is regenerated automatically by the firmware. The right place to manipulate BICO sources is through p9491 (BICO source object), p9492 (BICO source signal), and p9493 (BICO source bit) - or in StartDrive via the BICO editor (right-click → Disconnect all).

Drive Operating States Relevant to the Error

The SINAMICS G120 state machine is published in the SINAMICS G120 Parameter Manual and the SINAMICS G120 Operating Instructions. The transitions relevant to this fault are:

The reported symptom - the user cannot leave the commissioning state because the drive automatically reverts on each download attempt - is the firmware's safety behavior. When StartDrive injects parameters that the state machine cannot validate while commissioning is active (specifically the BICO source list and the free-telegram layout), it rolls back to p0009 = 1 (Quick commissioning).

A separate but related state to watch is p0010 (commissioning parameter filter). While p0010 ≠ 0 the firmware blocks writes to a subset of parameters including the entire BICO list - exactly the parameters reported in the user's fault rotation.

Free Telegram versus Standard Telegram

The user is using a free PROFINET telegram (that is, Siemens telegram type "free PZD-12/12" or similar). Free telegrams are configured via:

• p0922 = 999 (free telegram selection)
• p2079 (PROFIdrive PZD telegram extended setpoint/strobe bit)
• p2051[0..n] - list of PZD sent to the controller (drive inputs)
• p2061[0..n] - list of PZD received from the controller (drive setpoints)

The length of these lists must agree with the StartDrive project and with the device configuration in HWCN (TIA Portal → Devices & Networks → PROFINET interface → Telegram configuration). A mismatch of even one PZD causes the firmware to reject the next sub-index write because the slot has not yet been allocated.

For an encoderless fan application the conventional telegram mapping is:

The user opted out of this with a custom telegram. As long as the count n in p2051/p2061 matches StartDrive's offline list and the BICO source list p9462 is properly populated before the telegram is initialised, the download succeeds. Reordering the BICO list after the free telegram is commissioned is what triggers the rotating SubIndex error.

Step-by-Step Resolution Procedure

1. Save the project. TIA Portal → Project → Save As, including the StartDrive plug-in data. Keep a backup of the offline parameter set (.par) by exporting the online drive via StartDrive "Upload to PG".
2. Read the current drive firmware. Connect online, navigate to Configuration → Commissioning → Overview and note the firmware string under "Drive firmware version". Compare to the offline project (V4.7.13). If they differ at SP level (V4.7 SP13 SP1 vs SP2), install the matching Support Package in TIA Portal.
3. Force the drive to Ready. Open Configuration → Commissioning → Overview in StartDrive. The status panel must show Ready (green LED, ZSW1 bit 0 = 1). If the drive is in Quick commissioning, complete the wizard. If the wizard closes itself - the symptom reported by the user - clear p0009 and p0010 manually to 0 in the parameter table.
4. Temporarily switch to standard telegram 1. Set p0922 = 1 (standard telegram 1, two PZD), save the parameters to the drive EEPROM (p0971 = 1), and acknowledge with the "Copy RAM to ROM" button in StartDrive. This resets the BICO list length to a known good state before the free telegram is re-installed.
5. Re-import the project BICO data. Reconnect StartDrive, open the BICO editor, right-click → Disconnect all. Reconnect the application's BICO sources one by one in the order: control word, status word, setpoint chain, ramp-function generator, then outputs. Commit with "Download to device (RAM)" only - not "Download to ROM".
6. Restore the free telegram. Set p0922 = 999, re-populate p2051[0..n] and p2061[0..n]. Click the StartDrive "Reload telegram" button and verify the new telegram appears in the device view.
7. Save permanently. In StartDrive, choose Drive → Save data to memory card (ROM). Confirm with the parameter p0971 = 1 in the parameter table; the drive acknowledges with F-A0187 "Save All Parameter to ROM" for approximately 3 seconds.
8. Power-cycle the Control Unit. Pull the 24 V supply for at least 30 s, then re-energise. After power-up the LED must show Ready, not Commissioning.
9. Download again. Run StartDrive "Download to device" once more. The SubIndex alarm must not reappear.

Alternative Recovery: Manual Parameter Reset

If the drive refuses to leave the commissioning state because the BICO list is permanently corrupted in RAM, perform a factory reset of the application class and re-bring the drive up cleanly:

1. Set p0009 = 30 (factory reset - commissioning parameter filter).
2. Set p0976 = 1 (start the factory reset of all parameters).
3. Wait for the drive to show F-A0186 ("Reset of all parameters to factory setting") with state = DONE (LED flashes).
4. Once the drive returns to "Ready", re-launch StartDrive's quick commissioning, choose the same motor and application class (Encoderless speed control, fan), and enter the data from the original project.
5. Before reopening the free telegram, copy RAM to ROM (p0971 = 1) and then download the project in two passes (BICO first, free telegram second).

Verification

After completing the resolution procedure, confirm the following on the running system:

The trace facility is the most useful verification tool: open StartDrive → Trace and add p9462[0], p9462[22], p0010, p0922 and r0002. Capture a 30-second window. If p0010 momentarily returns to a non-zero value during the download, the SubIndex error will repeat.

Firmware Compatibility Notes

The mismatch between StartDrive showing V4.7.13 and the physical drive showing V4.7 SP13 SP2 is one of the most common reasons for a rotating SubIndex error on a CU240E-2 PN. Use the following matrix to choose the right StartDrive version:

Loading HSP0311 SP2 into TIA Portal V16 Update 5 brings the project in sync with the drive. The Support Package is also available on the Siemens Industry Online Support portal. For long-term stability, upgrade the Control Unit firmware with the official SINAMICS firmware package via the Web server or the StartDrive "Update firmware" wizard. Do not downgrade a CU240E-2 PN from V4.7 SP13 SP2 to V4.7 base - the Safety kernel and the BICO sub-index tables are not backward-compatible.

Common Edge Cases

Edge case 1 - drive with Safety Integrated telegram

If the CU240E-2 PN is commissioned with PROFIsafe, an additional BICO layer is activated (p9500, p9610, p9620) and p9462[] is expanded. After a Safety acceptance test the drive must be re-initialised with p9761 → 0 and the parameters committed with the Safety password (p9762).

Edge case 2 - second Control Unit from a different project

If the CU was formerly used in a different machine, the StartDrive data stored in non-volatile memory still holds the previous BICO layout. Clear the project with "Reset drive to factory settings" before commissioning.

Edge case 3 - encoderless fan load with pump curve

Pump and fan applications (G120 "P" application class) add p1220, p1221 and p1226 to the BICO chain. They share indices with the regular ramp-function generator. After the first download, confirm p9462[22] shows the expected control-word bit (typically bit 0 of STW1).

Edge case 4 - StartDrive multi-user / TIA-multi-user project

In multi-user TIA Portal projects the StartDrive data may be stale relative to the local edit. Right-click the drive in the project tree → "Reload from project" before the download; otherwise the download sends an empty BICO list and the firmware creates empty sub-indices that fail validation on the next pass.

Related Fault Codes and Alarm Codes

Codes A01841 and F08505 are the two most useful early indicators - they appear immediately before the rotating SubIndex errors described in this article. If they are missing in the alarm history but the SubIndex error persists, suspect a corrupted parameter file on the offline project rather than the drive.

FAQ