ET 200iSP Random I/O Loss: Affected Modules and Firmware Fix

Problem Overview

SIMATIC ET 200iSP stations installed in PCS 7 systems (V8.x and V9.x) deployed in process-industry plants have exhibited a recurring, intermittent failure mode in which one or more I/O modules appear to "drop" from the rack without a corresponding diagnostic buffer entry. The PROFIBUS or PROFINET interface module (IM 152-1 / IM 152-1PN) reports the slot as failed, the channel LEDs on the affected module go dark, and downstream signals (DI, DO, AI, AO) are lost to the AS 410H automation station. Power cycling the rack, or physically reseating the module against the backplane bus module, restores communication — sometimes for weeks, sometimes for hours — before the same slot fails again.

The pattern is symptomatic of a known backplane bus contact problem on a specific production window of ET 200iSP I/O modules shipped between 06/2007 and 06/2008. Siemens documented the issue internally and published an updated IM firmware (referenced in Siemens Industry Online Support entry ID 21344491) under the heading "faults on the backplane bus." In parallel, the manufacturer executed a hardware-replacement program for affected modules within the affected serial-number range.

Affected ET 200iSP Module Population

The table below lists every SIMATIC ET 200iSP I/O module identified by Siemens as part of the affected production window. Note that the failure is bound to Product Version (PV / FS), not simply to the order number: a 6ES7 131-7RF00-0AB0 module with PV 1 or PV 6 is not in the affected scope, even if it shipped in the 2007–2008 window.

Symptoms and Diagnostic Signature

Each of the following indicators has been confirmed in the field on PCS 7 V8.x systems using an AS 410H redundant pair and ET 200iSP racks on PROFIBUS DP:

1. Random module dropout: One I/O slot transitions from OK to failure without a corresponding SF (group fault) LED on the module itself illuminating — the module simply disappears from the IM's slot map.
2. No diagnostic buffer entry on the IM 152: The PROFIBUS diagnostics from the IM report a station failure but no module-level diagnostic record, which masks the root cause from standard STEP 7 / PCS 7 online diagnostics.
3. Mechanical restoration: Gently pressing the module toward the backplane bus unit, or pulling the module out and reseating it, clears the fault within a single PROFIBUS scan cycle.
4. Power-cycle workaround: Removing and reapplying the 24 V DC power to the rack reliably restores communication.
5. Multi-plant replication: The fault appears in geographically unrelated installations running identical hardware revisions, ruling out site-specific causes such as EMC, grounding, or vibration.
6. Intermittent cadence: Failures may occur at a rate of one per month for several months, then go silent — creating a false sense of resolution before the next dropout.

Root Cause

Siemens attributed the failure to the mechanical contact system between the I/O module and the ET 200iSP backplane bus module. Within the affected serial-number range, the contact spring force on the module's bus connector degrades below the threshold required to maintain a reliable connection under the rack's normal thermal cycling and minor mechanical stress. The fault is therefore:

• Hardware-bound — it cannot be cleared by reconfiguration, re-parameterization, or PROFIBUS re-addressing.
• Mechanical in nature — reseating the module mechanically re-establishes the contact, which is why the fault appears to clear spontaneously.
• Independent of firmware revision on the I/O module — the firmware resides on the IM 152-1 / IM 152-1PN side, not on the affected I/O boards.

The updated IM firmware referenced in Siemens Support entry 21344491 improves the diagnostic granularity and station-restoration behavior so that transient bus-contact losses are recovered automatically rather than presenting as a hard slot failure. However, the firmware update alone does not restore the mechanical contact on the affected I/O modules — the long-term resolution is hardware replacement of the modules within the affected serial-number range.

Identification Procedure

Before contacting Siemens for module replacement, perform the following site-side qualification steps. Document the results so the Siemens support engineer can match the order numbers, product versions, and serial numbers against the affected-population database.

1. Open HW Config in STEP 7 / PCS 7 and read out the order number and FS (firmware status / product version) of every ET 200iSP I/O module in each rack.
2. Cross-reference each module against the Affected Module Population table above. Flag any module whose product version matches an entry.
3. Read out the serial number of every flagged module. In HW Config, right-click the module → Object Properties → Identification. The serial number is a 10-character alphanumeric string beginning with the production date code (e.g., S C-Jxxxxxx for 2007, S M-xxxxxxx for 2008).
4. Compile a fault log for each rack over a 30-day window. Capture timestamp, slot number, IM diagnostic buffer content, and operator action (if any) that cleared the fault.
5. Photograph the module label including the production date code and serial number, and forward the full list to the local Siemens representative with the support entry ID 21344491 referenced.

IM Firmware Update Procedure

Siemens issued an updated firmware load for the ET 200iSP interface module (IM 152-1 and IM 152-1PN variants) to improve the rack's tolerance of transient backplane-bus contact interruptions. Update the IM firmware on every ET 200iSP rack in the affected plants before — not after — module replacement, so that the rack remains operable during the swap-out window.

Prerequisites

• STEP 7 V5.5 + SPx or TIA Portal V15.1 or later with HSP for ET 200iSP installed.
• SIMATIC S7 FW Update Tool (part of the STEP 7 / TIA Portal installation) or the standalone FW Update Tool accessible via the menu Target system → Firmware update.
• Online connection to the AS 410H (or S7-400) over PROFIBUS / PROFINET — the firmware is loaded into the IM via the fieldbus, not via the backplane bus.
• Documented slot assignment and PROFIBUS address for each IM 152.

Step-by-Step Firmware Load

1. Open the SIMATIC project in STEP 7 / TIA Portal and establish an online connection to the target AS.
2. Navigate to Online → Accessible nodes and identify the target IM 152 by its PROFIBUS address or PROFINET device name.
3. Select the IM 152 and choose Target system → Firmware update from the menu bar.
4. Browse to the firmware container file (.upd) supplied by Siemens for the corresponding IM article number (e.g., 6ES7 152-1AA00-0AB0). Verify the file's checksum against the value published in the Siemens support entry.
5. Confirm the target slot — only the IM is updated; the I/O modules below the IM are not affected by the IM firmware load.
6. Start the update. The IM reboots automatically once the load completes.

Verification After FW Update

1. Confirm the IM returns to RUN, with the SF and BF LEDs off.
2. In HW Config, read the new firmware version under Object Properties → Identification and confirm it matches the expected update level.
3. Cycle power on the rack to verify the new firmware survives a cold restart.
4. Force one DI / DO channel per affected module type through PCS 7 and confirm end-to-end propagation to the operator station.

Module Replacement Path

The firmware update reduces but does not eliminate the failure rate on affected hardware. The definitive corrective action is to replace every module that matches both the order number, the product version, and the serial-number range. Field experience across multiple plants confirms the following sequence:

1. Compile the affected population list using the Identification Procedure above.
2. Open a support case with Siemens referencing entry 21344491, attach the population list, and request a goodwill / warranty replacement.
3. Order replacements on a 1:1 basis plus one spare per module type for commissioning flexibility. Lead times for the affected order numbers in 2024–2026 typically run 6–10 weeks; place orders early.
4. Schedule the swap-out during a plant turnaround, not during continuous operation. Even though the IM firmware update allows transient recovery, the affected modules will continue to drop out and create spurious process alarms during a running batch.
5. Update the HW Config to the product version of the replacement modules, recompile, and download to the AS.
6. Return the replaced modules to Siemens for failure analysis if requested under the support case.

Hardware Replacement Verification

After each module is swapped, perform the following local verification before moving to the next slot:

Fault Matrix for Triage

Prevention and Field Recommendations

• Inventory your fleet: Run the Identification Procedure across every ET 200iSP rack in every plant, even if no failure has been reported. Plants that have not yet experienced the fault will, statistically, hit it within 1–3 years of the affected modules being placed in service.
• Apply the IM firmware update proactively on all racks, not only the affected ones. The improved recovery behavior reduces spurious process alarms even on unaffected hardware.
• Avoid redundant triggering: Many site teams chase the symptom by replacing power supplies, PROFIBUS cables, and even the AS 410H before identifying the root cause. A 10-minute cross-reference of order number and product version against the table above saves weeks of misdirected troubleshooting.
• Document the affected population in your CMMS / SAP PM so that future maintenance windows can plan the replacement without a crisis.
• Engage Siemens with the entry ID: When opening a support case, always cite 21344491. This routes the case to the team familiar with the issue and avoids the first-line triage loop of "check your grounding" or "check your PROFIBUS termination."

Notes on PCS 7-Specific Behavior

The fault surface differs slightly between standard SIMATIC S7-400 applications and PCS 7 process-control applications. In PCS 7, the I/O dropout propagates as follows:

1. The IM 152 reports the slot failure as a station diagnostic on PROFIBUS DP / PROFINET.
2. The AS 410H sets the channel-level QBAD flag in the process image.
3. The CFC block receiving the signal interprets QBAD=1 and propagates the substitution value downstream.
4. The WinCC faceplate displays the maintenance / invalid flag with the configured quality color.
5. If the affected signal is part of an interlock or a closed-loop controller, the PCS 7 standard "Out of Service" handling takes over — controllers go to manual, binary outputs adopt their configured safe-state value.

For PCS 7 installations in hazardous-area (Ex zone 1 / 21) service, the ET 200iSP is typically the only viable distributed-I/O platform because the intrinsically safe barriers are integrated into the module. The replacement module population is therefore non-optional: there is no drop-in substitute from a different product family.

When to Escalate Beyond the Standard Procedure

Escalate the support case to Siemens Industry Online Support if any of the following apply after the firmware update and module replacement have been completed:

• Dropouts continue on modules that are not in the affected product-version list.
• The IM 152 itself is generating spurious station-failure diagnostics without a corresponding slot-level event.
• The PROFIBUS DP / PROFINET diagnostic buffer contains entries referencing 0x0E (slot fault) without an accompanying module-side diagnostic record.
• The failure rate does not return to zero after the swap-out, indicating an additional environmental cause.

Frequently Asked Questions