Applicable Systems
MicroLogix
CompactLogix
ControlLogix
PowerFlex
Symptoms
The controller's OK LED turns solid red. A major fault is displayed in the controller properties in Studio 5000. The controller halts program execution and all I/O is placed in its configured fault state.
Possible Causes
- Memory parity error in the controller's internal memory
- Controller hardware failure
- Power surge or transient damaged internal memory
- Electrostatic discharge (ESD) event near the controller
Troubleshooting Steps
- Step 1: Connect to the controller via Studio 5000 and read the major fault code
Confirm the fault is a memory parity error (type 16#0001) - Step 2: Power cycle the controller to see if the fault clears on reboot
Fault clears and controller returns to normal operation - Step 3: If the fault persists, re-flash the controller firmware
Firmware update completes and controller starts normally - Step 4: If the fault still persists, replace the controller module
New controller operates without memory errors
How to Reset
To reset: 1) In Studio 5000, go to Controller Properties > Major Faults and clear the fault. 2) If the controller does not respond, perform a firmware re-flash. 3. If hardware replacement is needed, install the new controller and download the project. Caution: Memory parity errors often indicate hardware degradation, so schedule a replacement proactively.
Common Replacement Parts
- 1789-L10: CompactLogix 5370 L1 controller (Match the catalog number to the existing controller)
Frequently Asked Questions
- Q: What is a memory parity error?
A memory parity error means the controller detected data corruption in its internal memory, typically caused by hardware failure or power transients.
- Q: Should I replace the controller after a parity error?
If the error persists after a firmware re-flash, yes. Recurring parity errors indicate permanent memory degradation requiring hardware replacement.
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Source: Rockwell Automation CompactLogix 5370 User Manual, Publication 1756-UM522
Category: PLC & VFD
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