Fixing ET 200SP 'Difference in Lower Level Component' TIA Error

Problem Overview

The diagnostic message "Difference in lower level component" appears in the TIA Portal when an online connection is established to a SIMATIC ET 200SP station but the offline project on the engineering station no longer matches the runtime configuration on the CPU. On the affected CPU the diagnostics view shows a yellow exclamation mark next to the rack icon, and the operator panel warning column lists the difference as a "configuration difference" rather than a hardware failure.

This symptom is reported frequently on the CPU 1512SP-1 PN with order number 6ES7512-1DK01-0AB0, which is the standard PROFINET controller/decentral I/O controller variant of the ET 200SP distributed PLC. The error is, in the vast majority of cases, a software/project synchronization problem and not a defective CPU module. Typical user complaints include:

• "CPU icon shows a yellow triangle with a different number of submodules."
• Online disappears immediately after a successful Go Online.
• Online/Offline comparison highlights >90% of blocks in red.
• Force download is greyed out despite STOP command.
• Recent project restore did not match the SD card contents.

The remainder of this article classifies the underlying causes, details the diagnostic workflow inside the TIA Portal, and prescribes reproducible corrective procedures. Where applicable, the article references the official Siemens Industry Online Support portal for product manuals (Equipment Manual SIMATIC ET 200SP CPU 1512SP-1 PN) and the online help of TIA Portal V15.1 to V19.

Product Identification: ET 200SP CPU 1512SP-1 PN (6ES7512-1DK01-0AB0)

Before diagnosis, confirm the part number on the front flap of the CPU module and on the packaging label:

The exact catalogue number matters: 6ES7512-1DK01-0AB0 is the standard variant. The fail-safe F-version is 6ES7512-1DK01-0YB0 (CPU 1512SP-1 F PN), the engineering ordering suffix differs and changes the licensing of safety programs but does not change the diagnostic behavior covered in this article.

Root Cause: Configuration / Project Mismatch

The TIA Portal maintains two parallel representations of the controller:

• Offline project – the configuration in the engineering project (.ap15 / .ap18) used for programming on the laptop.
• Online project – the live configuration loaded in the CPU at this moment, including the device configuration that was downloaded last.

The string "Difference in lower level component" is generated by the online-check routine when the offline tree and the online tree of the same CPU object diverge. The TIA Portal enumerates the lower-level stations/submodules of the CPU, compares counts, names, slot numbers, order numbers, and firmware versions, and reports the first divergence.

Categories of causes

1. Project drift – the offline project was created/copied from a different CPU, or an existing project was edited on the engineering station after the last download.
2. Hardware insertion in the field – slots were swapped, replaced, or extended without rewriting the project.
3. Firmware mismatch – an I/O module was upgraded in the field (or a module from an older residual stock was inserted) without updating the device configuration in TIA Portal.
4. SD-card swap – a service-card inserted into the CPU differs from the one referenced by the offline project (different serial, different article number, or simply the user's SD slot has nothing).
5. CPU replacement – the CPU was replaced in the panel but the offline project still contains the original serial number; the COM/Profibus/Profinet assignments are still aligned, but the CPU descriptor is different.
6. Different TIA Portal version – the project was written by TIA V17 and is opened with TIA V15.1; some properties cannot be deserialized and the offline tree is incomplete.

Items 1, 5 and 6 dominate the field reports. The error message does not tell which category applies; the analyst must trigger an explicit Compare Online/Offline command.

Diagnostic Workflow in TIA Portal

Apply the following workflow whenever an ET 200SP station raises the warning:

1. Switch the engineering station into the project that owns the CPU.
2. Open the project tree and double-click Project > Devices & networks.
3. Right-click the CPU 1512SP-1 PN object and select Go online (shortcut Ctrl+K). The Go Online button may initially display "Online connection is being established".
4. Wait for the handshake: the icon above the CPU changes from grey to either a green tick (online and matching) or a yellow exclamation mark (online with differences).
5. Right-click the CPU again and choose Compare Online/Offline. The comparison editor opens in a new tab.

The compare editor is the authoritative source for the difference list. Typical output looks like:

A red dot or yellow dot on the Online/Offline compare tab combined with green on the Blocks tab means only the hardware configuration is drifting.

Locating the exact deviation

1. Open the Online/Offline compare result.
2. Switch to the Detailed comparison drop-down filter Only show differences.
3. Expand the rack: ET 200SP Station > IM Module > Slot 0...15.
4. The first slot highlighted in red is the offending position. The right-hand pane explains the difference (e.g. "Module differs: order number 6ES7131-6BH00-0BA0 → expected 6ES7131-6BF01-0BA0").

If the CPU does not respond at all, the diagnostic path is different (see the network section further below).

Resolution: Choice Between Download and Upload

Once the analyst has the comparison result, two macro-paths are valid depending on who has the right version of the project.

Path A – Offline project is the master (Download to device)

1. Bring the CPU to STOP using the online toolbar or the operator panel (toggle the mode selector to RUN → STOP; wait for the RUN LED to extinguish, the STOP LED to light). For safety-related CPUs (F-versions) STOP must be entered before any write.
2. Right-click the CPU and select Download to device > All.
3. TIA Portal performs a consistency check; if it passes, the wizard opens. Confirm the target subnet and click Load.
4. When prompted, click Overwrite all (the project will replace both the program and the hardware configuration on the CPU).
5. Restart the CPU if needed. If the F-CPU is involved a re-passivation is mandatory after download.

Path B – Live PLC project is the master (Upload from device)

1. The user has the live plant program but no matching offline project.
2. Right-click the CPU and select Upload from device. TIA Portal will offer Upload station to PG/PC with the option to upload the device configuration only, the entire program, or a selection.
3. Select Upload station, set the path under Target path, and start. The project tree is rebuilt locally.
4. Compare again to confirm.

Once either path completes, the Compare Online/Offline command must show all green ticks and the warning "Difference in lower level component" no longer appears after a re-Go-Online.

Resolving Hardware-Linked Differences

When the yellow exclamation mark reappears immediately after a complete download, the lower-level configuration must be fixed at the project level. The most common scenarios are documented below.

Slot inserted in the field

A hot-swap or maintenance action added a module that the offline project does not know about. Detection: Open Device view in the TIA Portal, drag-and-drop the same module on the same slot (same order number, same FW), then re-download. The CPU accepts configuration changes during RUN with no restart for I/O modules that support CiR (Configuration in RUN); the ET 200SP IM 155-6 PN ST from FW V3.0 supports CiR via the slot-empty placeholder PROFINET > ET 200SP > STS.

Firmware version mismatch

The project has been opened for a different module version, for example an analog input card was upgraded from FW V0.1 to V0.4. TIA Portal blocks the download. Procedure:

1. Right-click the module in the device view.
2. Select Properties > General > Module identification.
3. Click Read from device if the module is online, or update the FW version manually against the printed label.
4. Recompile and download.

Wrong device type inserted in slot

When the slot number is correct but the order number differs, for example a 6ES7131-6BF01 replaces a 6ES7131-6BD00, re-drag the correct module from the catalogue onto the slot. TIA Portal reports the structure drift in the Verify compilation step before download.

PROFINET device still complains

On the ET 200SP the decentralised I/O sits behind an IM 155-6 PN. Differences in the IM devices will trigger the same warning. Open the IM under the PROFINET subnet, refresh the device list and compare.

Firmware Considerations and TIA Portal Version Compatibility

Mixing firmware versions between the offline project and the running CPU is one of the cheapest-to-clear causes. The standard recommendation matrix for the CPU 1512SP-1 PN is:

If the CPU is at FW V2.0 and the offline project was built for V2.9, the project will load but the visualisation/Online view will flag "different revision" warnings, which is the same family of mismatch as the lower-level difference.

Updating the firmware follows the official procedure described in the equipment manual: Online > Accessible devices > Right-click CPU > Online & Diagnostics > Firmware update. The user account must be in the administrator/security group Maintenance Engineer with the right Firmware download enabled in the project security settings.

Network / Connectivity Prerequisites

The error "Difference in lower level component" is one face of a larger family of online issues. Before reinstalling the project, validate the Ethernet path:

1. IP address – the CPU has a static IP or a reserved DHCP entry on the subnet. Use Online > Accessible devices to discover the device; the displayed MAC must match the label.
2. Subnet mask must match the engineering station's. Online requires that the node can reach X1 (default IP 192.168.0.1 when unset).
3. PROFINET topology – the controller is configured in the project. If the device is on a different ring or a different VRRP domain, the device-level discovery hides.
4. CPU to RUN – the CPU mode has to be at least not in defect state. If the CPU is in STOP with the SF LED solid, fix the underlying system error first.
5. Online port – ports TCP/102 (S7CommPlus) and UDP/34964 (PN-DCP) must not be blocked.

If the CPU does not respond to Accessible devices, the problem is connectivity, not configuration drift; the warning would not appear at all, the online button would timeout after 60 s.

Handling the SD Card as Part of the Project

The ET 200SP CPU supports the SIMATIC Memory Card (SMC) but the CPU 1512SP-1 PN variant has its own SIMATIC Memory Card called the SIMATIC Memory Card up to 32 GB (6ES7954-8HC0x-0AA0). When the card is replaced or inserted after startup, the CPU treats that operation as a different lower-level component. Typical solutions are:

• Always use the same SMC that the offline project points to. The path appears in Project tree > Online & diagnostics > SIMATIC memory card.
• If the SMC has the latest project (downloaded to it via the file browser), the CPU on power-up uses the SMC content as the master.
• Remove the card only with the CPU in STOP, otherwise the card's file system can be left in an inconsistent state.
• Format the SMC via Online & Diagnostics > SIMATIC memory card > Format before reuse.

Step-by-Step: Safe Force-Download Procedure

Use this procedure when the project is so far drifted that TIA Portal refuses a normal download. The procedure forces the CPU into a clean state, then loads the offline project.

1. Open the project, ensure the CPU 1512SP-1 PN is the highlighted object.
2. Switch the operator panel selector to STOP.
3. Online > Accessible devices > verify the CPU appears with its correct IP/MAC.
4. Right-click the CPU > Download to device > Hardware and software.
5. If the option is greyed out, choose Compile to project memory first (Project > Compile > Hardware + software).
6. In the download dialog tick Reset CPU, which empties all M/DB/retentive areas and forces a fresh load.
7. Confirm the IP subnet and click Load. TIA Portal will issue a full STOP > Loading > RUN restart.
8. Watch the diagnostics: the SF LED should extinguish within 30 s. The MR (maintenance required) may stay on briefly while diagnostics re-evaluate.
9. Run Compare Online/Offline: must be fully green.

Verification Checklist

After completing the corrective action, run the following quick checks to confirm the warning is gone and the system is healthy.

1. In the project tree, navigate to Online & Diagnostics of the CPU; the diagnostics buffer should no longer contain the entry Lower level component mismatch.
2. Toggle the operator switch from STOP to RUN. Watch the CPU's RUN LED — solid green within 5 s for a healthy project.
3. In the compare editor run Online/Offline compare; the report must be entirely green.
4. Open the Watch & force tables (Watch_1 by default). Force a test tag to 0/1 to verify the watch interface is live.
5. Trigger a re-detect via Online > Accessible devices on PROFINET device list. All devices in the live subnet must show status "OK" with green ticks.
6. Pull the operator switch to RUN. Verify the application's HMI screen reflects field values (e.g. tags from DIs).
7. Take a backup of the current project to the SIMATIC Memory Card and store one copy on the engineering file share for rollback.

A healthy station returns the four diagnostic states shown in the table:

Troubleshooting Matrix

Preventive Measures

Once the configuration matches, the following practices keep the project in sync:

• Maintain a single offline project source-of-truth per machine and store it under version control (GIT, TIA Multiuser, or a controlled file share).
• Apply the rule "only one person writes, all read" for the master image; or use TIA Portal Multiuser Server instead of free-for-all project sharing.
• Never change hardware (swapping a module, adding/removing a card) without first committing the offline project change to the engineering server.
• Always download the entire project ("Hardware and software") rather than partial block changes after major maintenance.
• Take a SIMATIC Memory Card backup after every successful download.
• Document the firmware versions and update the project readme with the TIA Portal version used.
• Run Online/Offline compare as a release-step before delivering code to production.

These recommendations are consistent with the Siemens Industry Online Support service notes on consistent engineering, particularly the application notes about project consistency in SIMATIC S7-1200/1500 controllers.

FAQ