Resolving S7-1200 Retentive Data Error 16#02:4009 on S7-1214 (6ES7214-1AG40-0XB0) Firmware V4.2

An S7-1200 CPU drops to STOP, clears all retained tags, and posts a diagnostic event with ID 16#02:4009 to the diagnostic buffer. On the affected unit — a SIMATIC S7-1214 DC/DC/DC with order number 6ES7214-1AG40-0XB0 running firmware V4.2 — the diagnostic entry reads literally "CPU error: Retentive data error: Real-time clock initialized" and ends with the CPU mode line "Stop". This article decodes the event, ranks the root causes observed in the field, and walks through the recovery paths Siemens support recommends for V4.2 hardware.

Affected Hardware and Firmware

Decoding Diagnostic Event 16#02:4009

The diagnostic buffer stores each entry as a DWORD. The high word (W#16#0002) classifies the event as a CPU fault tied to operating-mode transition. The low word (W#16#4009) is the specific fault code that, in the S7-1200 system manual event table, corresponds to "Retentive data inconsistent — the CRC of the retained data area does not match the expected signature at startup". The associated text "Real-time clock initialized" is a parallel symptom: the same NVRAM region that stores retained M bits, DB instances, and counters also holds the RTC backup. When the area is declared invalid, the firmware defaults the clock to 01-01-2011 00:00:00 and the RTC must be re-set.

From the S7-1200 system manual (function manual "CPU Memory"), the retentive area is backed by an internal SuperCap plus, on most S7-1214 boards, an optional coin cell (CR1025 on older hardware, BR2032 on the 6ES7214-1AGxx series). The SuperCap alone holds retentive data for a minimum of 20 days at 25 °C after a configured power-off, provided the capacitor was fully charged. The coin cell extends the hold-up time to roughly 1 year.

The error is recoverable and is not in itself a hardware defect — it is a firmware-and-software disagreement about whether the NVRAM contents are still trustworthy. That framing is the key to selecting the correct remedy.

Root Cause Analysis

Five root causes account for the majority of 16#02:4009 events observed on the 6ES7214-1AG40-0XB0 platform. Rank by probability for an in-service fleet that has not been touched in years:

1. Firmware bug 4.2.0 NVRAM handling. Siemens' V4.2.1 release notes explicitly cite improvements to internal NVRAM CRC verification for certain memory components. If multiple CPUs of the same batch are exhibiting the same event, the firmware hypothesis is the strongest.
2. Power-loss during a buffered write. The retained area is written to in fixed pages. A brown-out shorter than the configured buffer time but long enough to disturb the page write produces a CRC mismatch on the next start.
3. RTC coin-cell exhaustion. The 6ES7214-1AG40-0XB0 board carries a socketed coin cell. Once the cell drops below 1.8 V, the SuperCap is the only retention source, and the margin against a power event collapses.
4. Excessive AC ripple on the 24 V supply. The S7-1200 hardware installation manual specifies that the 24 V supply must not exceed 35 VDC and must not contain more than 5 % peak-to-peak AC ripple of nominal (1.2 Vpp on 24 V). A high-ripple supply can corrupt the NVRAM write strobe.
5. Instruction-version / project-version mismatch. TIA Portal auto-increments instruction versions on download. If a project has been migrated across multiple TIA versions and re-downloaded, the firmware may discard retained instances that the new instruction version does not recognize.

Pre-Work and Safety

1. Open TIA Portal, go to Online & Diagnostics → Diagnostic Buffer, and click Save as text. The export is the only artifact that proves the event to Siemens support.
2. Open the project's PLC → Properties → Retentive Memory page and screenshot the exact number of retentive M bytes, retentive DB instance bytes, and the RTC enable flag. This is the configuration you must restore.
3. Capture the current RTC time, the IP address, the PROFINET device name, and any active security password. A factory reset wipes the IP/name, and an S7-1200 protected by an access password cannot be re-loaded without that password.
4. Disconnect and lock out hazardous process energy. After a retentive memory reset, retained tag defaults can change actuator states on the first scan.
5. Verify the 24 V supply with an oscilloscope set to AC coupling at the CPU's power terminals. Confirm < 1.2 Vpp ripple and < 35 V peak.

Solution Path A — Memory Reset and Retentive Area Rebuild

This is the minimal, lowest-risk recovery path. Use it when a single CPU has shown the event once and the firmware is already at 4.2.1 or later.

1. In TIA Portal, right-click the device → Online & Diagnostics → Functions → Reset to factory settings. Confirm the prompt. The CPU must be in STOP for this to take effect.
2. Power-cycle the CPU (off for 10 s, then on). The CPU comes up with a blank retentive area and a defaulted RTC.
3. Set the RTC: Online & Diagnostics → Functions → Set time of day. In PLC code you can also issue WR_SYS_T from a startup OB.
4. Re-download the project. TIA Portal rebuilds the retentive area from the configured offsets in the device configuration. Retained values will all be their declared initial values, not the values from the last running session.
5. Read the diagnostic buffer and confirm 16#02:4009 does not appear on this restart.

Per the TIA Portal cloud documentation, clearing retentive memory before a download is achieved by resetting the CPU to factory settings first; a download on top of an uncleared retentive area only refreshes the program, not the retention map.

Solution Path B — Firmware Update from V4.2.0 to V4.2.1 (or Later)

Siemens' first-line response to a repeat 16#02:4009 on the 6ES7214-1AG40-0XB0 is to update firmware. Use this path when (a) the event recurs after a clean memory reset, (b) multiple CPUs from the same batch show the event, or (c) the diagnostic buffer contains a chronologically repeating trail of 16#02:4009 separated by normal operation.

1. Identify the current firmware exactly: Online & Diagnostics → General → Firmware. The version string is reported as V4.2.0, V4.2.1, etc. A 6ES7214-1AG40-0XB0 can take any V4.x firmware in the same major; the firmware is keyed to the order number, not the serial number.
2. From the Siemens Industry Online Support portal, search for the firmware update tool. The article ID for the S7-1200 firmware updater is referenced under the S7-1200 FAQ entry on retentive memory errors. Save the .upd file to a folder reachable by the engineering station.
3. Place the CPU in STOP. Do not power-cycle during the update.
4. Run the S7-1200 firmware updater. Enter the target IP. Browse to the .upd file. Click Update firmware. The tool will report progress in percent; a full flash of an S7-1214 takes 90 to 180 seconds.
5. After the updater reports success, the CPU reboots with the new firmware and an empty retentive area. Re-execute Path A from step 2.
6. Re-download hardware configuration and software. Re-set the RTC.

Solution Path C — Power Quality and RTC Battery Service

If the firmware is current and the event still recurs, treat the cabinet and the battery before suspecting the CPU itself.

24 V supply

• Measure the DC voltage at the CPU's power terminals with a true-RMS DMM and with an oscilloscope. Confirm 20.4 to 28.8 VDC steady state.
• AC-couple the scope and verify < 1.2 Vpp ripple. A high-ripple supply on a power supply with no industrial-grade filter will produce CRC errors even on a healthy CPU.
• Verify PS fault and overload LED states. A SITOP or third-party supply in current limit during inrush can sag the 24 V rail long enough to disturb a write.

RTC coin cell

• On the 6ES7214-1AG40-0XB0 the coin cell is accessible by removing the lower terminal cover; the socket is on the main board.
• Measure the cell voltage under a 100 kΩ load. A fresh CR1025 reads 3.0 V; replace below 2.5 V.
• Replacements: 6ES7291-8BA20-0AA0 is the official Siemens battery module; an off-the-shelf CR1025 with solder tabs is functionally equivalent.
• After cell replacement, set the RTC and run a controlled power-down test (off for 60 s; on; verify retained tags survived).

Verification Procedure

1. After the chosen recovery path, power-cycle the CPU three times with 30-second hold times.
2. Read the diagnostic buffer after each cycle. Event 16#02:4009 must not reappear. If it does, the residual cause is firmware or hardware — escalate to Path B with a fresh firmware, then to RMA if Path B fails.
3. Force each retained tag from the project, then restart, and confirm the tag holds the forced value. A pass proves both the NVRAM path and the retentive map.
4. Leave the CPU in RUN for a 72-hour soak under normal process load, then re-check the buffer for the event.
5. Document the firmware version, the RTC, the supply ripple, and the cell voltage in the maintenance log. A repeat of the same event 90 days later is a maintenance-of-record problem, not a repeat-fault problem.

Troubleshooting Matrix

Field-Proven Caveats and Edge Cases

• Five-CPU batch syndrome. A common report is "four of five identical CPUs work; one does not". In every confirmed case the outlier is the one with the lowest SuperCap charge at install time. A factory reset + firmware update + 24-hour powered standby brings the SuperCap to full charge and resolves the majority of those single-CPU failures.
• Hidden retentive area in DB instances. Marking a DB as Retain in TIA Portal does not by itself preserve its values across a retentive data error — the firmware declares the whole NVRAM region invalid and zeroes it. Plan for a cold-start initialization routine in OB100 for any retained DB that drives safety logic.
• Password lockout after factory reset. A factory reset on an S7-1200 with an access password does not erase the password; it erases the program and the IP. The PLC remains inaccessible without the password. Confirm the password in the project before resetting.
• RTC drift as an early warning. If the RTC drifts by more than a few seconds per day, the coin cell is suspect. Treat RTC drift as a soft precursor to a 16#02:4009 event.
• Multi-CPU memory card migration. Moving a SIMATIC memory card from a 4.2.0 CPU to a 4.2.1 CPU does not migrate retentive values. The card contents are read once at startup; a different firmware version will reject the card as inconsistent.
• PROFINET device name. A factory reset reverts the PROFINET device name to its factory default of <empty>. Re-assign the device name via TIA Portal or PRONETA before the IO controller attempts AR establishment, or expect a PROFINET diagnostic storm on top of the retentive event.
• Event appearance during a stop-and-restart sequence. A programmed STOP-to-RUN transition that coincides with a process-driven write burst can produce a transient 16#02:4009 even on a healthy CPU. Confirm the event in the buffer is from a real power-loss signature (long timestamp gap, RTC reset) and not from the programmed transition.

Reference Data

Related Diagnostic Events Worth Knowing

Engineers troubleshooting 16#02:4009 frequently encounter the following adjacent events. They share the same retention area but point to different recovery paths:

• 16#02:400A — Memory card removed while CPU in RUN. Reinsert the same card; do not swap to a freshly formatted card without a project download.
• 16#02:400B — Memory card write error. Replace the SIMATIC memory card (6ES7954-8LF02-0AA0 family).
• 16#02:400C — Memory card type mismatch with the project. Re-format the card or use the card Siemens shipped for the firmware version.
• 16#02:400D — User program on card is incompatible. Re-download the project.
• 16#03:4301 — RTC drift, distinct from 4009. Battery problem rather than retention problem.

FAQ