Applicable Systems
Modicon M221
Modicon M241
Modicon M251
Modicon M340
Modicon M580
Altivar
Symptoms
The PLC STATUS LED turns red. The controller detects a memory fault. Internal RAM or flash memory has failed a read/write operation or checksum verification.
Possible Causes
- Battery-backed RAM failure
- Flash memory wear or corruption
- Memory access violation in user code
- Power surge damaged memory hardware
Troubleshooting Steps
- Step 1: Read the memory fault details in EcoStruxure Control Expert
Confirm the fault type and affected memory region - Step 2: Attempt to re-download the application to flash memory
Application downloads and verifies correctly - Step 3: Replace the controller battery if RAM is affected
New battery maintains RAM contents during power cycles - Step 4: If the fault persists, replace the controller CPU module
New controller has no memory faults
How to Reset
To reset: 1) Re-download the application. 2) Replace the battery if needed. 3) If the fault persists, replace the CPU. 4) Reset the application. Caution: Memory faults often indicate hardware degradation, so plan for replacement.
Common Replacement Parts
- BMXXBATO200: Modicon M340 backup battery (Replace every 2-3 years to prevent data loss)
Frequently Asked Questions
- Q: How do I know if the battery needs replacing?
The PLC will log a low battery warning before the battery fails completely. Replace the battery as soon as the warning appears to prevent RAM data loss.
- Q: What happens if the flash memory is corrupted?
The controller cannot boot the application. You need to re-download the application from EcoStruxure Control Expert. If re-download fails, the flash memory hardware may be permanently damaged.
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Source: Schneider Electric Modicon M340 Hardware Guide, 2023
Category: PLC & VFD
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