Resolving S7-400 Bus Fault (Bus1F) and Missing IE General in Station Configurator

An active Bus1F (Bus Fault 1) LED on an S7-400 CPU indicates that one or more decentralized I/O stations (ET 200M/SP) configured on the fieldbus cannot be contacted or do not physically exist. To resolve a missing 'IE General' network adapter in the Station Configuration Editor, select the PC Station in SIMATIC Manager and execute 'PLC -> Configure' to register the component, followed by downloading connections via NetPro. Furthermore, if WinCC Runtime displays 'Connection status: Disconnected' (Abgebaut) on a raw TCP/IP channel, reconfigure communication to use the certified PCS 7 standard: Named Connections via access point PC Internal.

Diagnostic Meaning of S7-400 Bus Fault (Bus1F) LEDs

On Siemens S7-400 and CPU 410-5H controllers, the Bus1F (Bus Fault 1) and Bus2F LEDs monitor the physical and logical integrity of integrated fieldbus subnets (PROFIBUS DP or PROFINET IO).

When Bus1F illuminates solid red or flashes, the CPU's internal master system has detected an uncontactable slave. In bench-testing or partial commissioning environments where an engineer downloads a full plant hardware configuration without having all physical ET 200 remote racks powered and connected, Bus1F is completely normal and expected. The CPU logs OB86 (Rack Failure) and OB82 (Diagnostic Alarm) events in its diagnostic buffer until the physical hardware matches HW Config.

Resolving Missing IE General in Station Configuration Editor

On the PC Station (Operator Station or Engineering Station), the Station Configuration Editor (Komponenten-Konfigurator) manages virtual hardware slots representing the WinCC application and network interface cards (such as IE General or CP 1623).

If IE General is missing from the Station Configuration Editor after creating it in HW Config, the offline STEP 7 station definition has not been deployed to the Windows kernel. The engineer must execute the two-step station provisioning workflow: first, running PLC -> Configure... from SIMATIC Manager to register the components; and second, executing a NetPro download to transfer IP routing and connection parameters.

Named Connections vs Raw TCP/IP Channels in WinCC

A foundational tenet of SIMATIC PCS 7 (documented in Compendium Part A, Chapter 9.4) is that WinCC Operator Stations must never use the raw TCP/IP channel unit under SIMATIC S7 Protocol Suite. The table below highlights why:

Raw TCP/IP Limitations: Requires manual IP and rack/slot parameterization inside WinCC, lacks redundant server routing, and does not support high-resolution ALARM_8P event packets.
Named Connections Architecture: Standard PCS 7 architecture. The communication channel is bound to access point PC Internal. Connections are established symbolically using names compiled directly from NetPro, providing fault tolerance, automatic driver diagnostics, and certified APL performance.

Comparison of Network Interface Setup Steps

The table below details diagnostic symptoms, root causes, and corrective actions for PC Station commissioning faults.

Fault PhenomenonUnderlying Root CauseCorrective Engineering ActionS7-400 Bus1F Lit RedConfigured remote I/O slaves missing on busConnect physical field hardware or disable offline slaves in HW ConfigIE General Missing in SCEStation component not configured locallySelect PC Station in SIMATIC Manager -> PLC -> Configure...SCE Component Shows Yellow WarningName mismatch between STEP 7 and SCERename station in SCE to match exact name in SIMATIC ManagerWinCC Status: Disconnected (Abgebaut)Using raw TCP/IP instead of Named ConnectionsMigrate channel to Named Connections via PC Internal in NetProNetPro Download FailsSimatic Shell not bound to Terminal BusSet correct NIC in Simatic Shell -> Settings on both stations

Step-by-Step Procedure to Restore PC Station Communication

Follow this procedure to resolve missing station components and establish live Named Connections:

Deploy Station Configuration to SCE:
- On the OS computer, open the Station Configuration Editor: verify that the station name matches the SIMATIC Manager PC Station object name exactly.
- In SIMATIC Manager on the ES, right-click the OS PC Station object and select PLC -> Configure....
- Select the target computer and click Configure: this pushes the virtual rack layout (WinCC Appl. in Slot 1, IE General in Slot 2) to the OS.
Download NetPro Connections:
- Open NetPro: ensure the S7 Named Connection from the OS to the AS is compiled.
- Highlight the OS PC Station and select PLC -> Download to Current Project -> Selected Station.
Configure Access Point in Set PG/PC Interface:
- In Windows Control Panel on the OS, open Set PG/PC Interface.
- Verify that access point CP_H1_1: points to the physical network card, and access point S7ONLINE points to PC internal (local).
Recompile OS and Launch WinCC:
- Compile the OS in SIMATIC Manager: ensure Named Connections is selected as the network path.
- Download the OS project, open WinCC Explorer, and start runtime: verify that connection status displays 'Connected'.

Verification

Verify communication health through the following checks:
1. In the Station Configuration Editor, confirm that both WinCC Appl. and IE General display run status (green icons) without diagnostic symbols.
2. In WinCC Explorer, open Tag Management -> SIMATIC S7 Protocol Suite -> Named Connections: right-click the AS connection -> Connection Status and verify status is 'Connected'.
3. In CFC online test mode, verify that process tag values match live readings in WinCC process graphics.
4. In the S7-400 diagnostic buffer, confirm that no communication connection faults are logged.

Limitations and Operational Precautions

Never rename a PC Station in Windows System Properties without updating STEP 7 HW Config, the Station Configuration Editor, and Simatic Shell simultaneously. Mismatched station names instantly invalidate local DCOM security tokens and break NetPro download paths. Additionally, do not attempt to clear Bus1F faults by deleting OB86 from the CPU program; missing error organization blocks will cause the CPU to enter STOP mode when a real bus fault occurs.

Engineer FAQ

Will the S7-400 CPU stop if Bus1F is active?

No, provided organization blocks OB86 (Rack Failure) and OB122 (I/O Access Error) are loaded in the CPU. The CPU continues running but flags unreached I/O addresses as bad.

Why does PCS 7 forbid using the standard WinCC TCP/IP driver?

The standard TCP/IP driver cannot process PCS 7 chronological ALARM_8P messages and does not support S7-400H redundant controller communication. Named Connections are required for PCS 7 DCS functionality.

What should I do if 'PLC -> Configure' reports that the station cannot be found?

Check name resolution and Simatic Shell multicast settings. Verify that the ES and OS can ping each other by computer name over the Terminal Bus.

Technical References

Related Tags

Bus1F
Station Configuration Editor
IE General
Named Connections
PC Internal
NetPro

Bus1F

Station Configuration Editor

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Resolving S7-400 Bus Fault (Bus1F) and Missing IE General in Station Configurator