An S7-400 CPU416-2 DP entered a frozen state with the RUN and STOP LEDs flashing. Its diagnostic buffer reported “Frequency of recognized and corrected memory errors.” A power cycle restored operation, but the message continued for about one day before disappearing. The available evidence does not identify a confirmed root cause, affected firmware version, or power-supply fault.
Separate Observations from Possible Causes
| Item | Evidence status | Engineering implication |
|---|---|---|
| CPU416-2 DP froze | Observed | The event interrupted normal CPU operation. |
| RUN and STOP LEDs flashed | Observed | Record the LED state with the diagnostic buffer evidence if the event returns. |
| Power cycling restored operation | Observed | This recovered the CPU but did not establish the cause. |
| Memory-error message persisted for about one day | Observed | A continuing diagnostic indication remained after recovery and then disappeared. |
| No known site change introduced electromagnetic interference | Reported condition | This rules out a known change, not every possible interference or hardware cause. |
| Firmware defect | Hypothesis | No firmware version or confirmed corrective release is provided. |
| Power-supply defect | Unconfirmed | The evidence does not directly implicate the power supply. |
Choose the Correct Maintenance Action
Do not replace the power supply solely from this diagnostic message because no supporting power-supply symptom is documented. Immediate CPU replacement is defensible only when recurrence risk is unacceptable or additional evidence identifies the CPU as faulty. Otherwise, preserve the diagnostic evidence and use controlled monitoring to determine whether the event repeats.
- Save the complete diagnostic buffer and record the CPU identification, installed firmware, module configuration, LED pattern, and event time before another power cycle clears useful context.
- Review whether Siemens identifies a firmware correction applicable to the installed CPU and firmware. Do not treat an unspecified firmware update as a confirmed fix.
- If an applicable update is verified, check compatibility with installed communications and function modules before deployment. For a redundant installation, keep the paired CPUs at the required compatible firmware level.
- After the approved change—or without a change if no applicable correction exists—monitor for recurrence. The supplied recommendation proposes one week, but the evidence does not establish that period as a Siemens requirement.
- If the CPU freezes again or the same memory-error diagnostic returns, escalate with the saved buffers and configuration data; replace the CPU when the recurrence evidence or Siemens support diagnosis justifies it.
Control Firmware-Update Risk
A firmware update can be a reasonable diagnostic action only after matching the installed CPU to a documented correction. Confirm compatibility with every installed CP and FM before changing firmware, preserve the current project and configuration, and define a recovery method. The evidence supplies no firmware identifier, so selecting a target version without further documentation would be speculative.
Verify Recovery and Recurrence
Successful recovery means more than returning the CPU to RUN. Verify that the process and communications operate normally, capture the diagnostic buffer after restart, and check whether the memory-error message reappears. If another freeze occurs, compare its timestamp, LED state, and buffer entries with the first event; repeated matching evidence strengthens the case for CPU replacement, while power-supply replacement still requires independent supporting evidence.
FAQ
Should I replace a CPU416-2 DP after one corrected memory-error event?
Not automatically. Save the diagnostic buffer, verify whether an applicable firmware correction exists, and monitor; replace the CPU if the freeze or diagnostic recurs or a Siemens diagnosis identifies the CPU as faulty.
Does “Frequency of recognized and corrected memory errors” prove the power supply is bad?
No. The supplied evidence contains no voltage, power-supply diagnostic, or related symptom that identifies the power supply, so replacing it from this message alone is unsupported.
Should I update CPU416-2 DP firmware when RUN and STOP flash?
Update only after confirming that a documented correction applies to the installed CPU and firmware. Check CP and FM compatibility first, and coordinate both CPUs if the system uses a redundant pair.