S7-1200 TIA Portal V14 Connection Partner Not Responding Fix

1. Problem Definition

A SIMATIC S7-1200 CPU (e.g., 6ES7214-1AG40-0XB0, 6ES7215-1AG40-0XB0, or 6ES7216-3AD40-0XB0) is configured with IP 192.168.10.50 / subnet 255.255.0.0 and the engineering PC is configured with IP 192.168.10.100 / subnet 255.255.0.0. When the user attempts to "Go online" or perform a "Accessible nodes" scan in TIA Portal V14, TIA raises:

The same TIA installation is able to connect to other S7-1200 CPUs in the same network, so the engineering station, NIC, and TIA Portal installation are functional. The fault is therefore isolated to one specific CPU on the PROFINET segment.

The S7-1200 uses the PROFINET (IE) protocol on TCP/IP port 102 (ISO-on-TCP / RFC 1006 / S7Comm) for the PG communication channel. When the "connection partner is not responding" message appears, it means the TCP three-way handshake to port 102 of the CPU never completed within the default TIA timeout window (typically 10 s).

2. Network Topology & Address Analysis

3. Root Cause Categories

Siemens categorizes "Connection partner is not responding" errors in entry ID 109751654. The most common causes, in order of statistical frequency, are:

1. Project/online address mismatch — TIA is searching for the device at an IP that differs from the device's actual IP. This is the most frequent cause and is precisely what the dialog box warning text alludes to.
2. PG/PC interface assignment — The wrong NIC (e.g., Wi-Fi, virtual adapter, VPN TAP) is bound to the S7ONLINE access point.
3. PLC not in the same PROFINET subnet in the TIA project — TIA tries to route through a non-existent gateway.
4. Windows Firewall blocking TCP/UDP 102, 161, 34964, 49152–65535 — A Windows update or third-party security suite silently re-enables the firewall on the private profile.
5. Firmware / TIA version mismatch — The CPU firmware is newer than the version supported by TIA V14 (e.g., FW 4.5 was added in TIA V14 SP1 Update 6+; FW 4.6 requires TIA V16).
6. Duplicate IP — Another device on the segment is using 192.168.10.50, causing an ARP conflict and the CPU's TCP stack to stay in listen but never complete the handshake.
7. PROFINET interface disabled or in fault — Port physically damaged, link down, or port switched off in the device configuration.
8. CPU in STOP with security / access protection — Know-how protection or a password on the HMI/PG access level blocks the connection without a valid login.

4. Use "Accessible Nodes" Instead of the Project View

The fastest diagnostic is to bypass the TIA project navigator and scan the live segment. In the project tree:

1. Expand the project, right-click the CPU device (or "Online access" in older layouts).
2. Choose Online & Diagnostics.
3. In the Online & Diagnostics dialog, select Accessible nodes from the function tree.
4. Change the PG/PC interface type to PN/IE and select the correct physical NIC.
5. Click the green Start search button (magnifying glass).

If the CPU is physically responding on the wire, it will appear in the results table with its detected IP, MAC, and device type. The IP shown in the search result is the live address of the CPU — this is the IP TIA was actually probing in the failed "Go online" attempt. If the search returns "no devices found" as the user reported, the CPU is not answering DCP/LLDP probes at all, which moves the fault to the PLC or to the firewall on the PC side.

5. PG/PC Interface Assignment

TIA Portal V14 reads the S7ONLINE access point from the Set PG/PC Interface tool (Siemens Installation Path → Siemens Automation → SIMATIC → PG-PC Interface). Configure as follows:

1. Open Set PG/PC Interface.
2. Under Access Point, select S7ONLINE (STEP 7).
3. Under Interface Parameterization Used, choose the physical Ethernet NIC (e.g., Intel I219-V - TCPIP.1). Do not select Wi-Fi, Hyper-V, VMware, VPN, or virtual TAP adapters.
4. Confirm with OK. TIA Portal must be restarted to pick up the change.

Verify the binding from a Windows command prompt:

netsh interface show interface
route print
arp -a

Confirm that 192.168.10.50 resolves to the same MAC prefix you see on the CPU's front label. S7-1200 MAC addresses are in the range 00-0E-8C-xx-xx-xx or 28-63-36-xx-xx-xx (Hilscher / Siemens-assigned). A MAC from a different OUI is the first sign of a duplicate-IP collision.

6. PLC-Side Verification (Online via Direct Ethernet)

When TIA cannot reach the CPU, the most reliable PC-based check is to put the PG on the same /16 network with a point-to-point cable and use the CPU's MAC to ping the device even if the configured IP is suspect.

1. Open a Windows cmd with administrator rights.
2. Send a directed ARP request: arp -d 192.168.10.50 then ping 192.168.10.50 -w 2000.
3. If ping fails, perform a Layer-2 check using the Siemens Primary Setup Tool (PST) or the PRONETA tool (free download from Siemens, entry ID 109751635). PRONETA performs a network scan independent of TIA, displays all PROFINET devices, and lets you reset the IP of an unconfigured CPU.

If PRONETA finds the CPU at 192.168.10.50 but TIA does not, the fault is at the TIA / PC layer. If PRONETA does not find the CPU either, the fault is on the PLC side — see the firmware and access-protection sections below.

7. Windows Firewall and Security Software

TIA Portal V14 opens the following ports when communicating with an S7-1200:

1. Open Windows Defender Firewall with Advanced Security.
2. Confirm that SIMATIC TIA Portal and Siemens S7 Protocol are listed in Inbound Rules and Outbound Rules with Allow the connection.
3. Temporarily turn off the firewall on the Private profile and retry the Accessible Nodes scan. If the scan now succeeds, re-enable the firewall and add a precise inbound rule for TCP 102 from 192.168.10.100 to 192.168.10.50.
4. Disable third-party security software (Symantec Endpoint, McAfee, Kaspersky, Palo Alto Traps, CrowdStrike) and repeat the test. CrowdStrike and Traps in particular are known to block DCP broadcast frames silently.

8. Firmware and TIA Version Compatibility

Each TIA Portal version supports a specific range of S7-1200 firmware revisions. From the Siemens compatibility tool:

If the affected CPU was updated to FW 4.5 or 4.6 (e.g., the field engineer applied the latest firmware to address a separate bug) and the workstation still runs TIA V14, the CPU will accept the TCP connection only at the discovery level and the "Go online" step will hang or fail with the partner-not-responding error. Confirm the firmware on the CPU by reading the front display (CPU 1215C and 1216C only) or by checking the Module Information once Accessible Nodes succeeds.

The fix is one of:

• Downgrade the CPU to a compatible firmware using a SIMATIC Memory Card (article 109741209).
• Upgrade the TIA Portal installation to V16 or later on the engineering station.

9. Subnet Mask, Duplicate IP, and Physical Layer

A 255.255.0.0 subnet is valid for PROFINET (Siemens permits /8 to /30), but it creates a 65,534-host broadcast domain that can mask problems caused by a duplicate IP. Run a Layer-2 scan with PRONETA or arp -a to verify that exactly one MAC owns 192.168.10.50.

Additional physical-layer checks:

• Inspect the PROFINET port LEDs (Link and Activity). Both should be solid green; Activity should blink on PG traffic.
• Replace the patch cable and try a different switch port.
• Eliminate managed switches with PROFINET filtering enabled, IGMP snooping, or BPDU guard — these can block DCP frames.

10. Access Protection and Know-How Protection

The S7-1200 supports per-CPU access protection on the HMI/PG communication channel. With a password set for the "HMI/PG access" level, anonymous online connections are rejected. The CPU still answers DCP and is visible in Accessible Nodes, but the "Go online" attempt returns the partner-not-responding error.

To clear this, in the device configuration of the CPU in TIA, open Properties → General → Protection → Connection mechanisms and either remove the password or assign a known password, then reattempt the online connection. If the project password is lost, the only recovery is a factory reset of the CPU using a SIMATIC Memory Card with a fresh project — see 109741209.

11. Step-by-Step Recovery Procedure

1. Open Set PG/PC Interface; bind S7ONLINE (STEP 7) to the physical Ethernet NIC. Restart TIA Portal.
2. From the Windows command prompt, run ipconfig /all and confirm the PG has 192.168.10.100 / 255.255.0.0 on the correct adapter (not virtual, not VPN).
3. Launch PRONETA from the Siemens PRONETA installation; let the network scan complete. Note the IP and MAC of every PROFINET device.
4. Verify only one device owns 192.168.10.50. If a duplicate exists, disconnect that device and re-test.
5. From the same PC, in TIA Portal open Online access → [NIC] → Accessible nodes and click Start search.
6. If the CPU appears, right-click it and select Online & Diagnostics to download the existing project, then click Go online in the project tree. Confirm firmware and protection state.
7. If the CPU does not appear, disable the Windows Firewall (Private profile) and the third-party security suite, and repeat step 5.
8. Power-cycle the S7-1200 (MRES is not required) and observe the Link LED on the PROFINET port. After ~25 s the CPU should be reachable on its configured IP.
9. Cross-check the CPU firmware against the TIA V14 compatibility table in Section 8. Upgrade or downgrade as required.
10. Save the project, perform a full Download to device, and run the verification test in Section 12.

12. Verification

After the recovery, prove the connection is stable with the following checks:

• Online & Diagnostics → Diagnostics buffer: Open the buffer; it should be empty of PROFINET/TCP faults and should show a recent "Online connection established" event.
• Go online → Monitor / Force table: Add a tag from the default tag table; toggle it and observe the change in the live value column. This proves bi-directional S7Comm traffic.
• Compile and download: Run Project → Compile → Software (rebuild all) followed by Download to device → Hardware and software. The download should complete with status "Download successful (0:0:0)".
• Firmware consistency: In Online & Diagnostics → Module information, record the article number (e.g., 6ES7214-1AG40-0XB0) and firmware version (e.g., V4.4.0). Cross-check with the TIA compatibility table.
• End-to-end ping test: From the PG, run ping 192.168.10.50 -t for 60 s; no timeouts are acceptable.

Troubleshooting Matrix