Troubleshooting Siemens SINAMICS S120 Fault F31885 Encoder 1 DRIVE-CLiQ Error

Siemens S120 drive showing Fault F31885? This cyclic data transfer error means your encoder and Control Unit are out of sync. Learn how to check cables, shielding, and DRIVE-CLiQ connections.

 

In high-precision motion control applications using the Siemens SINAMICS S120, the DRIVE-CLiQ interface is the digital "nervous system" that connects your motor encoders to the Control Unit (CU). If you are seeing Fault F31885, this system has been compromised.

Fault F31885 indicates a Cyclic data transfer error. Essentially, the Control Unit and the Sensor Module (encoder) are no longer "shaking hands" in perfect synchronization. The drive has detected that the data telegrams are missing, arriving out of order, or failing to acknowledge the "sign-of-life" bit that ensures a safe, continuous connection.

Common Causes of F31885

This fault is almost always related to the physical integrity of the DRIVE-CLiQ communication path. Common culprits include:

• Cabling Issues: Damaged, pinched, or loose DRIVE-CLiQ cables.
• Electromagnetic Interference (EMI): Poor cable routing—specifically, running DRIVE-CLiQ cables too close to high-power motor leads or contactors.
• Shielding Failure: The cable shield is not properly grounded, allowing electrical noise to corrupt the high-speed data stream.
• Hardware Failure: A faulty Sensor Module or a damaged DRIVE-CLiQ port on the Control Unit.

Step-by-Step Troubleshooting

1. Inspect the Physical Connection

The first step is always the physical link. DRIVE-CLiQ connectors are robust, but they must be fully seated.

• Check the connectors at both the Sensor Module (on the motor) and the Control Unit.
• Ensure the locking tabs are engaged. A loose connection will cause intermittent F31885 trips.
• Look for debris or metal filings inside the port.

2. Verify Cable Integrity

If the connection is tight, the cable itself might be the issue:

• Swap the cable: If you have a spare DRIVE-CLiQ cable, swap it out. This is the fastest way to rule out internal wire fatigue.
• Check Routing: Ensure the DRIVE-CLiQ cable is separated from motor power cables by at least 200mm. If they must cross, they should do so at a 90-degree angle.
• Check for Wear: In robotic or moving applications, check the cable inside the cable carrier (drag chain) for signs of insulation wear or sharp bends.

3. Check for EMI (The Silent Killer)

If the fault occurs only when the drive is running (or specifically during high acceleration), it is likely interference:

• Ensure the DRIVE-CLiQ cable shield is properly terminated and clamped at the drive/cabinet entry point.
• Ensure the motor is properly bonded to the cabinet ground with a low-impedance connection.

4. Isolate Hardware

If you have checked the cables and the fault remains, isolate the hardware:

• If you have a multi-axis system, swap the Sensor Module with one from a known-working axis.
• If the fault follows the Sensor Module, the module is defective.
• If the fault stays on the original axis, the issue is likely the port on the Control Unit.

How to Reset Fault F31885

Once you have physically inspected the cables and verified the connection, you can acknowledge the fault:

• Perform a power cycle of the Control Unit (24V DC supply).
• Use the [Reset] command via your engineering software (STARTER or Startdrive) or the digital input configured for fault reset.

Maintenance Tip

F31885 is often an "early warning" fault. Before it becomes a permanent F31885, you may see intermittent communication warnings (A31885). If you see these warnings, investigate your cable routing immediately before the drive stops your entire production line.