Applicable Systems
MicroLogix
CompactLogix
ControlLogix
PowerFlex
Symptoms
The OK LED turns red. The controller reports a user program checksum error. The program in the controller memory does not match the expected checksum, indicating corruption.
Possible Causes
- Memory corruption due to power loss during program download
- Electrical noise corrupted controller memory
- Firmware bug caused memory write error
- Hardware memory failure
Troubleshooting Steps
- Step 1: Read the major fault code in Studio 5000
Confirm the fault is a checksum error (type 16#0004) - Step 2: Attempt to re-download the project to the controller
Project downloads successfully and checksum matches - Step 3: If re-download fails, perform a firmware re-flash
Firmware update completes and project can be downloaded - Step 4: If the error persists, replace the controller hardware
New controller accepts the project without checksum errors
How to Reset
To reset: 1) Clear the major fault in Studio 5000. 2) Re-download the project. 3) If the error persists, re-flash firmware and retry. 4. If hardware is suspected, replace the controller. Caution: Checksum errors may indicate failing memory, so plan for hardware replacement.
Frequently Asked Questions
- Q: What causes a program checksum error?
Memory corruption from power loss during downloads, electrical noise, firmware bugs, or hardware memory failure can alter the program and cause a checksum mismatch.
- Q: Is a checksum error a sign of failing hardware?
If the error recurs after re-downloading the project and re-flashing firmware, yes. It likely indicates permanent memory degradation in the controller.
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Source: Rockwell Automation CompactLogix 5370 User Manual, Publication 1756-UM522
Category: PLC & VFD
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