S7-1200 Memory Card Error 16#02:4175: Load Memory Corruption Fix

Problem Description

The SIMATIC S7-1200 CPU enters a permanent STOP state with a startup inhibit set after a power-off/power-on cycle. The diagnostic buffer fills with three sequential events that, taken together, identify a corrupted internal load memory structure. The condition is not transient: even after a second power cycle the CPU does not recover and a standard project download via TIA Portal is rejected. Only a factory reset followed by a clean retransfer of the hardware configuration and software restores operation, and even then the fault may recur within 24-48 hours if the underlying download method is not corrected.

Typical reported symptoms:

• CPU works correctly after the initial commissioning download.
• Power cycle within minutes or hours: CPU restarts normally.
• Power cycle the next day (cold start, full discharge of internal capacitors): CPU enters STOP with a startup inhibit and all three error LEDs (STOP flashing, MAINT flashing, ERROR steady) illuminated.
• Online > Compile and download objects is accepted by TIA Portal but the CPU does not leave STOP.
• Reset to factory settings is the only way to clear the inhibit.

Affected Hardware and Firmware

The fault has been reproduced and reported on at least the following configurations:

Diagnostic Buffer Interpretation

Read the online > Diagnostics > Diagnostic buffer of the CPU in STOP. The fault is identified by a triplet of Event IDs issued in this order. Any missing entry means the failure has a different root cause (e.g., hardware defect, watch-dog).

The ORID (Object Reference ID) of the 16#02:4046 entry is not a stable cross-platform diagnostic: Siemens does not document it as user-relevant and the same physical corruption can produce different ORID values between firmware revisions. Use the ORID only to confirm that the 16#02:4046 entry was raised by the same fault, not as a repair key.

The AID is always 16#00000000 for this class of internal load-memory corruption. Any non-zero AID is evidence that the failure is in the configuration of an I/O module or technology object, not in the load memory itself.

Root Cause Analysis

Two independent root causes reproduce the symptom set. They can occur together.

1. Download of "Program blocks only" with online delta transfer

The default TIA Portal download (Online > Download to device > Software (only changes)) performs a delta transfer: it writes only the blocks that have changed since the last successful transfer, leaving the previous block headers and re-load lists on the internal load memory. On an S7-1200, the internal load memory is implemented as a managed flash file system that is updated by a transaction protocol. If power is removed while the transaction log is open, the file-system metadata is left in a state that the next boot interprets as a structural inconsistency, which raises 16#02:4175 and 16#02:4046 and blocks startup until the load memory is rebuilt.

The defect does not appear on the first power cycle because the active program is still in working memory. It appears on the next cold start when the boot loader attempts to re-hydrate load memory into working memory and finds the file-system table unreadable.

2. Out-of-tolerance supply voltage during inrush

A second contributor is the 24 V supply behaviour at CPU inrush. The S7-1200 draws a brief inrush peak above its steady-state current when the internal bulk capacitors charge. A weak or marginal supply (long cable runs, small DIN-rail PSU, shared supply with contactors or drives) sags during this inrush. The CPU sees a brown-out after the boot loader has already started writing to the file system, which produces the same 16#02:4175 + 16#02:4046 pair. The diagnostic distinction is that the supply-related case may also generate a 16#02:4521 (power supply fault) entry that the pure software-transfer case will not produce.

Solution Procedure

1. Read the diagnostic buffer and confirm the three-event pattern (16#02:400C, 16#02:4175, 16#02:4046 with AID=16#00000000). If the pattern is different, escalate to the Siemens S7-1200 system manual diagnostics section and stop here.
2. Remove any SIMATIC memory card from the CPU. The card slot is on the underside of the CPU; press to eject. The CPU must boot with no card inserted.
3. Reset the CPU to factory settings.
   • Method A (without card): Set the mode selector to STOP, power off, power on, and within 3 s of the STOP LED flashing, hold the mode selector in the MRES position for at least 6 s until the STOP LED flashes faster, release for under 1 s, then press MRES again for 6 s. The CPU performs a factory reset and is reachable with IP 192.168.0.1 (or the last PROFINET name-assigned IP).
   • Method B (with empty card): Insert a Siemens SMC (6ES7 954-8LF...) that is empty or freshly formatted. Power on; the CPU will accept the empty card and behave as factory-fresh.
4. Verify power supply quality before reloading. Measure the 24 V at the CPU terminals under no load and during a simulated inrush (e.g., switch the PSU on while watching the rail with an oscilloscope or a recorder with at least 1 kHz sample rate). The voltage must remain within 20.4 V to 28.8 V at all times, including the inrush transient. If the supply sags below 19 V, replace it with a Siemens SITOP PSU sized at 1.5x the calculated load.
5. Update TIA Portal to V11 SP1 Update 1 or higher and update the CPU firmware to V2.1.3 (or the latest V2 service pack available on the Siemens Online Support portal) using the TIA Portal Online > Diagnostics > Update firmware path. The V2.1 line contains file-system transaction handling fixes that reduce the chance of a torn write on brown-out.
6. Re-transfer using "Software (all blocks)" instead of the default delta. In the project tree, right-click the CPU > Download to device > Software (all blocks). Confirm that the dialog says "Download to device - All blocks" and that the action overwrites the existing program on the CPU. Wait for the "Download successful" message before removing the PG cable or the supply.
7. Optional but recommended for unmanned panels: after the project compiles, also write the program to a Siemens SMC and use the SMC as the boot source. Set the CPU's card behaviour to Transfer card or Program card in the CPU properties > Card configuration. This keeps an off-CPU copy of the load memory that the CPU can re-load after a brown-out without a PG.

Verification

1. With TIA Portal online, open the diagnostic buffer and confirm there is no 16#02:4175 entry. The buffer must show a clean sequence: power-on (16#02:4300), startup complete (16#02:4301), RUN mode (16#02:4302).
2. Power cycle the CPU with the supply switched off for at least 30 seconds. The CPU must come back in RUN within 5 s and the MAINT and ERROR LEDs must remain off.
3. Repeat the power cycle at four different intervals: 1 minute, 10 minutes, 1 hour, and 24 hours. A persistent failure after 24 h is the most common relapse window. A reliable fix must pass all four cycles.
4. Force a controlled brown-out by switching the supply on and off rapidly five times in succession. The CPU must not enter a startup-inhibit STOP. If it does, the supply is still marginal and the PSU must be replaced.
5. Confirm the active program by reading a known value (e.g., a tag linked to an input) and matching it to the online watch table.

Transfer Options Reference

Memory Card Behaviour on the S7-1200

The S7-1200 SIMATIC Memory Card (SMC) is a proprietary SD-form-factor card based on standard SDHC but with Siemens file-system extensions. Three behaviours are selectable in the CPU properties:

• None — the card is ignored; this is the only setting that does not touch the file system at boot.
• Transfer card — the card is used to push a project into the CPU on power-on; the CPU copies the project to internal load memory and the card is then ignored. Suitable for series commissioning.
• Program card — the card is the live load memory; the CPU executes the project from the card. Used when the internal load memory is too small for the project.

Setting the card type to Transfer or Program requires the CPU to write to or read from the SMC at every boot. A SMC that was ejected without an OS-level eject in TIA Portal (Online > Card management > ...) can leave an inconsistent file system on the card, which then propagates to internal load memory on the next boot. Always use the TIA Portal eject sequence.

Power Supply Checklist

Firmware Update Procedure

1. Open the project in TIA Portal V11 SP1 Update 1 (or later) and go online with the CPU.
2. Right-click the CPU in the project tree > Online > Diagnostics.
3. In the device diagnostics window, select Update firmware from the toolbar.
4. Browse to the firmware .upd file downloaded from the Siemens Online Support portal. The latest V2.x firmware for the 6ES7 21x-1xx30-0XB0 family is found under entry ID 6ES7214-1HE30-0XB0 > Support > Firmware.
5. Confirm the firmware version and click Update. The CPU enters STOP, flashes all LEDs, and restarts. Do not remove power during the update; a mid-update power loss bricks the CPU and requires RMA.
6. After the CPU returns, perform a Reset to factory settings (Step 3 of the solution procedure) and reload the project using Software (all blocks).

Permanent Prevention Measures

• Always use Software (all blocks) for any S7-1200 production transfer. Reserve Software (only changes) for the engineer's bench.
• Use a Siemens SITOP PSU (6EP1xxx-...) with at least 50% current headroom over the measured load.
• Add a SITOP buffer module (6EP1xxx-1A...) or DC UPS (6EP1xxx-3...) on the CPU branch to ride through short supply interruptions.
• Fit a Siemens SMC (6ES7 954-8LF02-0AA0 or higher, 4 MB minimum) and configure it as a Transfer card. The card gives the CPU a clean load-memory image to re-hydrate from after a brown-out.
• Keep TIA Portal at the latest service pack supported by the CPU firmware. For firmware V2.x the matching TIA Portal baseline is V13 SP1 or higher; TIA V11 SP1 is end-of-life and no further fixes will be released for it.
• Schedule a quarterly cold-start test on installed CPUs. Power off for 60 seconds, power on, verify RUN within 5 s. A failure on this test is the earliest possible warning of a recurring 16#02:4175.

Troubleshooting Matrix

Related Event IDs (Quick Reference)

FAQ