Simotion D425 DRIVE-CLiQ Port Failure: S120 Module Isolation

1. Problem Overview

A production machine built around a SIMOTION D425 motion controller feeding a SINAMICS S120 multi-axis drive line-up lost DRIVE-CLiQ communication on an aged (10+ year) installation. The line-side infeed (Line Module) reported a function-block fault, several I/O tags on the infeed stopped updating, and the motor actual-torque value could no longer be read. The fault remained after the operator replaced the DRIVE-CLiQ cable, the Line Module, and finally the SIMOTION CPU in three separate maintenance windows. Communication to the S120 multi-axis stack collapsed as soon as the fourth axis module (a Double Motor Module) was plugged into the topology.

This article reconstructs the field-validated diagnostic flow that identified a single failed DRIVE-CLiQ port on one axis module as the root cause, and consolidates the procedures, LED codes, and configuration checks required to recover a SIMOTION D425 with an S120 drive line-up.

2. System Topology Reference

The affected machine was wired in the standard daisy-chain topology that Siemens recommends for SIMOTION D4x5 with SINAMICS S120:

1. SIMOTION D425, DRIVE-CLiQ port X100/X101/X102 — controller end
2. Active Line Module (or Smart/Basic Line Module) on the first DRIVE-CLiQ drop from the controller
3. Double Motor Module #1 (axes 1 & 2)
4. Double Motor Module #2 (axes 3 & 4)
5. Double Motor Module #3 (axes 5 & 6)
6. Double Motor Module #4 (axes 7 & 8) — the failing component

On the SIMOTION D425, DRIVE-CLiQ ports are typically designated X100 through X105 on the unit's front panel. The first port (X100) is normally reserved for the infeed/Line Module so that the controller can directly read the line status (DC link voltage, line currents, infeed-ready feedback) on the high-priority bus segment.

3. DRIVE-CLiQ Fundamentals

DRIVE-CLiQ is a serial point-to-point link operating at 100 Mbit/s over standard RJ45-style connectors with shielded twisted-pair cabling. Each connected node stores its own identity in non-volatile memory; the controller learns the topology automatically at start-up and compares it against the configured topology in the project. A mismatch or a non-responding node generates a topology fault and the controller drops the affected axis from cyclic data exchange.

Key bus characteristics relevant to the diagnostic flow described here:

For commissioning diagnostics, the published SIMOTION Service and Diagnostics overview lists the LED flash codes used by every DRIVE-CLiQ component. Treat that document as the canonical LED reference for the S120 family.

4. Initial Symptoms on the Failing Machine

Three observable symptoms appeared together when the line-up lost DRIVE-CLiQ integrity:

1. Line Module function-block fault — the infeed's standard FB reported a fault feedback to the PLC program, indicating either a lost cyclic telegram or a topology mismatch on the controller-facing port.
2. Missing I/O tags on the infeed — the operator reported that the entire periphery image of the Line Module (DC-link voltage, line current, status word) was no longer updating in the HMI. The tags were present in the project but their values were frozen or held in their last valid state with quality flag "bad".
3. Motor actual torque unreadable — every axis downstream of the Line Module lost its torque actual value. Because torque is read cyclically over DRIVE-CLiQ status frames, a broken link to the Motor Module is the most common cause.

These three symptoms are textbook indicators of a DRIVE-CLiQ topology break somewhere on the chain. The line-side and torque signals live on different nodes, so the fault must be on a segment that is upstream of both — typically a single failed port that disconnects everything downstream from the controller's view.

5. DRIVE-CLiQ LED Status Reference

Every SINAMICS S120 module with a DRIVE-CLiQ port carries a two-color status LED (green/red, sometimes called "RDY" or the per-port link LED). On the SIMOTION D425, the RDY LED on the front panel reflects the controller's overall DRIVE-CLiQ health. The relevant states are:

When a single port fails red and the entire chain downstream of it disappears from the controller, the most efficient diagnostic is the systematic isolation procedure described in Section 6.

6. First-Line Replacements That Did Not Resolve the Fault

Before escalating to a topology walk-down, the maintenance team performed three conservative replacements in sequence. Each change was made in a separate production window to avoid masking intermittent faults. None of them restored communication:

1. DRIVE-CLiQ cable replaced between the SIMOTION D425 and the Line Module. A known-good spare of the same length and article number was used. Result: same fault.
2. Line Module replaced with a verified spare. Result: same fault. The replacement module showed the same missing I/O image and the same red RDY LED.
3. SIMOTION D425 CPU replaced with a re-image of the project (CF card swap). Result: same fault. The new controller, even with a freshly loaded project, could not see the infeed.

At this point the obvious single-point failures had been eliminated. The next move was a complete topology isolation: disconnect every DRIVE-CLiQ cable from the controller except the one going to the Line Module. With only the controller-to-Line Module segment active, the infeed came up cleanly. The fault therefore lived on a node downstream of the Line Module, not on the infeed or the controller themselves.

7. Step-by-Step Topology Isolation Procedure

The recovery sequence that identified the failed module is the recommended procedure for any DRIVE-CLiQ topology break on a SIMOTION D4x5 / SINAMICS S120 line-up. Execute it from the controller outward, one node at a time, and log the result at each step.

Step 7.1 — Establish the baseline

1. Power down the SINAMICS S120 line-up and the SIMOTION D425.
2. Disconnect every DRIVE-CLiQ cable from the controller except the one going to the Line Module.
3. Power up. Confirm the Line Module appears in the online topology view of SIMOTION Scout (or TIA Portal with the SINAMICS Startdrive plug-in) and that the I/O tags of the infeed update.

Step 7.2 — Add axis modules one at a time

1. Reconnect the next Motor Module in the chain (Double Motor Module #1) with its existing DRIVE-CLiQ cable.
2. Power up. Check the RDY LED on the new module and verify the controller sees both the Line Module and Motor Module #1 in the topology diagnostic view.
3. Repeat for Motor Modules #2 and #3. At this point, on the field machine in question, the line feed, axes 1 through 6, and all intermediate modules were reporting healthy.
4. Reconnect Motor Module #4 (Double Motor Module #4, axes 7 & 8) with its existing DRIVE-CLiQ cable. Power up. Result on the affected machine: the entire DRIVE-CLiQ chain collapsed. The RDY LED on module #4 and the downstream status of modules #1, #2 and #3 went red.

Step 7.3 — Cross-swap the suspect cable

1. Take the DRIVE-CLiQ cable that connects Motor Module #3 to Motor Module #4.
2. Swap it with a known-good spare of the same article number and length.
3. Power up. If the fault moves with the cable, the cable is bad. If the fault stays on the same port, the module is bad.

On the affected machine, swapping the cable did not change the symptom. The collapse continued to occur at the same position in the chain regardless of which cable was used. This isolated the failure to Motor Module #4 itself.

Step 7.4 — Test the port direction

1. Take the DRIVE-CLiQ cable that goes into Motor Module #4 and move it to a different DRIVE-CLiQ port on the same module (if a free port is available).
2. If a free port is not available on the suspect module, swap the incoming and outgoing cables between the failing module and a known-good neighbour to confirm whether the failure is on the incoming port of module #4 or the outgoing port of module #3.
3. On the affected machine, the swap confirmed the fault was on the incoming DRIVE-CLiQ port of Motor Module #4. The outgoing port of module #3 was healthy.

Step 7.5 — Replace the suspect module

1. Power down. Replace Motor Module #4 with a spare of the same order number and the same or higher firmware release.
2. Reconnect the original DRIVE-CLiQ cables in the original routing.
3. Power up. Verify the full topology is detected. Result on the affected machine: the machine started up flawless.

8. Root Cause: DRIVE-CLiQ Port Hardware Failure

The failure mode was a damaged DRIVE-CLiQ receiver/port on the input side of Double Motor Module #4. With a damaged input port, the module could not establish a link to Motor Module #3, and the controller interpreted the entire downstream segment as missing. The reason earlier interventions did not work was that the failure was:

• Not on the cable (cable swap did not change the symptom).
• Not on the Line Module (infeed was healthy when isolated).
• Not on the SIMOTION D425 (CPU swap did not change the symptom).
• Not on the outgoing port of the upstream module (cross-swap moved the fault back to the same port on module #4).

The single point of failure was the input port of Motor Module #4, which is a hardware-level fault inside the module. It could have been caused by ESD during a prior maintenance intervention, by contamination of the RJ45 contacts, by mechanical stress on the cable causing a single wire break, or simply by aging of the connector's internal magnetics on a 10-year-old installation.

9. Topology Reconfiguration After Module Replacement

Once the failed module is replaced, the SIMOTION project must reflect the new hardware. In the SIMOTION Scout or TIA Portal project:

1. Go online to the SIMOTION D425.
2. Open the SINAMICS topology view (DO > SINAMICS_1 > Topology).
3. Compare the detected topology against the configured topology. The controller will flag the replaced module with a topology warning even if the article number is identical, because the serial number of the new module differs from the configured one.
4. Accept the new topology or perform a topology comparison and download the new configuration. The exact menu path depends on the engineering tool version (Scout V4.x, Scout TIA, or TIA Portal with Startdrive).
5. Save the project to the CF card so that the next cold start accepts the new module without manual intervention.

The official Siemens maintenance documentation for the SIMATIC Drive Controller family describes the procedure for replacing a DRIVE-CLiQ component with an identical or different article number, and explains the steps for accepting the new component into the topology.

10. Verification After Repair

After the module swap and topology reconfiguration, run the following verification steps before returning the machine to production:

1. RDY LED check — every DRIVE-CLiQ component in the chain shows a steady green RDY LED at the relevant port and at the module's front panel.
2. Topology view — the online topology in Scout/TIA Portal lists every node with the correct article number, firmware version, and serial number, and the topology comparison reports no warnings.
3. I/O tag check — the Line Module's status word, DC-link voltage, and current actual values update cyclically in the HMI. The motor actual torque for every axis downstream of the previously failed module updates as well.
4. Function block fault clearing — the Line Module function block in the PLC program no longer reports a fault feedback. Clear any latched faults in the HMI and confirm the fault does not reappear on the next controller restart.
5. Axis motion test — jog each axis at low speed and verify that the actual position, actual velocity, and actual torque track the setpoints. A DRIVE-CLiQ port that is borderline (intermittent) may pass the topology check but fail under cyclic load.
6. Diagnostic buffer — read the SIMOTION diagnostic buffer and the SINAMICS fault memory to confirm no residual DRIVE-CLiQ-related entries remain.

11. Field-Proven Diagnostic Matrix

Use this matrix to triage DRIVE-CLiQ faults on a SIMOTION D4x5 / S120 line-up before performing a full isolation walk-down:

12. Best Practices and Preventive Measures

The failure on this machine was unavoidable given the age of the electronics, but several practices reduce the probability of a similar incident and shorten the recovery time when one occurs:

• Pre-terminated DRIVE-CLiQ cables only. Field-terminated cables with incorrect pin-out or shield termination are a common source of intermittent links. Use the Siemens article numbers specified in the SIMOTION D425 manual.
• Respect the minimum bend radius and the service loop guidance. Cables routed through cable carriers with too tight a radius develop wire breaks near the connector over time.
• Label both ends of every DRIVE-CLiQ cable with the port numbers (for example, "D425 X102 <-> M3 OUT"). On a multi-axis machine, mis-wiring after a maintenance intervention is a frequent cause of "phantom" topology faults.
• Stock at least one spare Motor Module of each type used in the machine, with firmware loaded. A 10-year-old machine whose modules are no longer in production should have its replacement spares pre-qualified against the project.
• Back up the project and the CF card image after every change. A known-good image shortens the CPU-swap step from hours to minutes.
• Run an annual DRIVE-CLiQ health check: read the diagnostic buffer for DRIVE-CLiQ warnings (CRC errors, telegram failure counters), inspect connectors for oxidation, and verify the topology CRC counters in the SINAMICS diagnostic page.
• ESD discipline when working near DRIVE-CLiQ ports. A discharged static pulse that an operator does not even feel can damage the PHY on a port and cause exactly the failure described in this article.

13. Documentation References

• SIMOTION Service and Diagnostics overview (PDF) — LED codes, diagnostic buffer entries, and DRIVE-CLiQ status indicators for SIMOTION controllers and SINAMICS S120 components.
• Replacing a DRIVE-CLiQ component — official maintenance procedure for accepting a replacement node into the topology of a SIMATIC Drive Controller / SINAMICS S120 system.

14. Frequently Asked Questions