Troubleshooting Sinamics G120C Profibus Errors on S7-1200

Troubleshooting Sinamics G120C Profibus Errors on S7-1200

When a SINAMICS G120C DP frequency converter reports "converter not reachable" and the TIA Portal V15 user program reports "Error in Lower-Level Component" with a Profibus fault, the symptom is the same but the root cause can sit in any of three layers: physical layer (cable, connector, terminator), data-link layer (DP address, baud rate, bus profile), or application layer (GSD, slot/module configuration, telegram mapping). This reference walks through the configuration described in the original report — an S7-1215C DC/DC/RLY with a SIPLUS CM 1243-5 (article number 6AG1243-5DX30-2XE0) talking to a 2.2 kW G120C FSA Profibus variant — and applies equally to the standard 6GK7243-5DX30-0XE0 master module.

1. Problem Description

The reported failure chain is:

1. TIA Portal V15 online view shows the SINAMICS G120C node in red and displays Not reachable.
2. The S7-1200 OB1 diagnostic buffer records Error in Lower-Level Component (IO device failure) with a Profibus diagnostic event.
3. The G120C operator panel (BOP-2 / IOP) shows fault code F08501 "Profibus connection fault" or F08502 "Sign-of-life failure" depending on the version of firmware.

The message means the CPU never received a valid Profibus DP frame from the configured slave address, so the CM 1243-5 marks the slot as faulty and the application program loses its process image. Diagnose in this order: physical layer → DP address → GSD/slot mapping → telegram assignment.

2. Affected Hardware and Reference Configuration

Verify every device against the configuration in TIA Portal: select the device in the project tree, press Online > Accessible nodes. If the G120C is not listed, the master cannot even see the slave — the fault is physical or addressing.

3. SINAMICS G120C DP Variants and Identification

SINAMICS G120C ships with three Control Unit families:

• CU230P-2 DP — pump/fan/Compressor variant (article suffix ..UF1 or ..UP1).
• CU240E-2 DP — universal variant with extended I/O.
• CU250S-2 DP — servo variant.

For 2.2 kW FSA in the universal family, the typical order number is 6SL3210-1KE17-5UF1. Always read the device nameplate; the PROFIBUS address is set on the CU's DIP switches, not from TIA Portal. Default address on a brand-new G120C is 3. Refer to the SINAMICS G120C operating instructions for the address map.

4. Profibus DP Topology and Termination

The CM 1243-5 and the G120C are both DP slaves of an S7-1200-as-master topology, i.e. the S7-1200 CPU drives the bus. Physical-layer checks to perform before touching software:

1. Cable type. Use shielded PROFIBUS cable (Siemens 6XV1830-0EH10 or equivalent) with characteristic impedance 150 Ω.
2. Connectors. Use 9-pin D-sub connectors with integrated terminating resistor (e.g. 6GK1500-0FC10, 6ES7972-0BA52-0XA0). Avoid insulation-displacement connectors on long runs.
3. Terminating resistors ON at both physical ends only. Both the CM 1243-5 (last device) and the G120C (last device) must have termination switched ON; intermediate devices must have it OFF. The G120C Control Unit has a slide switch on the PROFIBUS connector for this purpose.
4. Baud rate. CM 1243-5 auto-detects from 9.6 kbit/s to 12 Mbit/s. Default 1.5 Mbit/s is safe up to 400 m of cable; reduce to 500 kbit/s if the G120C is the only node beyond 200 m.
5. Shielding. Bond the cable shield at every connector with 360° contact. Do not rely on pigtails.

5. Common Root Causes of "Not Reachable"

In order of frequency on field calls:

6. Step-by-Step Troubleshooting Procedure

1. Verify physical layer. Power the G120C, observe the RDY and BF LEDs on the Control Unit. Solid BF means the slave cannot reach the master; flashing BF means the slave is on the bus but parameterisation failed.
2. Verify DP address. Read the CU address on the BOP-2/IOP (parameter p0918) or on the DIP switch. The address must match the value configured in TIA Portal under Device view > G120C > Properties > PROFIBUS interface > Address.
3. Confirm the master is transmitting. From TIA Portal, Online > Accessible nodes. If the master (CPU 1215C with CM 1243-5) appears but the G120C does not, the bus is alive but the slave is mis-configured or the address is wrong.
4. Check GSD import. The installed GSD must match or exceed the SINAMICS firmware version. Download the latest GSD from the SINAMICS G120 GSD/GSDML collection. Re-import under Options > Manage general station description files (GSD) in TIA Portal V15.
5. Verify slot structure. In the TIA device view the G120C must show at least slot 0 (PROFIdrive profile) and slot 1 (PZD telegram, default Standard Telegram 1 or Siemens Telegram 352). Confirm the same module order in the drive's STARTER/SIMOTION SCOUT project (or in the BOP via p0922).
6. Check the firmware of the CM 1243-5. The CM 1243-5 must be at firmware V2.1.0 or higher when used with newer G120C firmware (V4.7 SP3+). The firmware is updated via TIA Portal: Online > Accessible devices > CM 1243-5 > Online & diagnostics > Firmware update. See CM 1243-5 manual.
7. Adjust watchdog. Parameter p2045 on the G120C sets the PROFIdrive sign-of-life timeout; the TIA slot watchdog must be set equal or higher (default 300 ms is sufficient for most 1.5 MBd segments).
8. Recompile and download. After every change: Project > Compile > Hardware (rebuild all), then download to the CPU. Power-cycle the G120C if a GSD upgrade was performed.

7. TIA Portal V15 Diagnostics and Online View

Open the device view, right-click the CM 1243-5, and choose Online & diagnostics:

• Diagnostics buffer: Lists DP-master events. Look for DP slave failure with the configured DP address.
• PROFIBUS nodes: Lists every node currently visible on the segment with baud rate and live status.
• Slot diagnostics: Per-slot error codes. Hex 0x0F = "no module inserted", 0x1F = "configuration mismatch".
• I&M data: Identification & Maintenance records confirm the manufacturer, order number, and serial number read from the G120C at startup. If I&M is empty, parameterisation never completed.

For the user program side, use the standard RDREC and WRREC instructions to read out the diagnostic record index 0/1 from the drive. The most useful record is DS0 / DS1 (channel-related diagnostics) — the first two bytes identify the channel class, and the next two bytes give the error number in hexadecimal (e.g. 0x0008 = parameterisation fault, 0x000A = sign-of-life failure).

8. SINAMICS G120C LED and Fault-Code Reference

Key fault codes to expect when PROFIBUS fails:

Read the active fault via parameter r0947[0] and the time stamp from r0949[0]. Acknowledge with p3981 = 1 or via control word bit 7.

9. Telegram and Parameter Mapping

The default PROFIdrive telegram for a 2.2 kW G120C is Standard Telegram 1 (4 PZD words out, 4 PZD words in). If you selected Siemens Telegram 352 in TIA, the same drive parameters must be exposed by setting p0922 = 352 on the drive. The mapping table for Telegram 1 is:

If the slot configuration in TIA Portal does not match p0922 on the drive, the CM 1243-5 reports slot diagnostic 0x1F and the drive reports F08510. Make p0922 consistent with the slot you dragged from the hardware catalogue.

10. Firmware Compatibility Matrix

11. Verification and Commissioning Checklist

1. CPU 1215C reports No faults in the diagnostic buffer and the CM 1243-5 BF LED is OFF.
2. TIA Portal Accessible nodes lists the G120C at the configured DP address.
3. Device view shows Status: OK for the G120C node.
4. Watch table: write 16#047E (control word "OFF1 high, ramp enable") to the first PZD; the drive responds with ZSW1 = 16#0337 (ready, enabled, no fault).
5. BOP-2/IOP shows rdy and a positive actual speed when a setpoint is applied.
6. Fault buffer on the drive contains no entries after 10 minutes of cyclic operation.

If any of the six steps fails, repeat the troubleshooting tree in section 5 before concluding the installation is healthy.

12. Field-Proven Tips

• Always set p2045 to 3 × the bus cycle time when commissioning a long cable run; the default 300 ms is fine for <200 m at 1.5 MBd but marginal for slower baud rates.
• If the drive was previously configured via STARTER and is now driven by TIA, make sure the project stored in the drive (RAM to EEPROM) matches the TIA configuration. Otherwise the drive will boot with the old telegram and report a slot mismatch.
• Keep the PROFIBUS segment isolated from VFD output cables by at least 200 mm to avoid coupling common-mode noise that produces intermittent BF events even with perfect termination.
• Document the DP address in the cabinet door label so future commissioning engineers do not re-set the DIP switch and break an existing master.

FAQ