CompactLogix 5380 T03:C23 at Run: what to check first?
My CompactLogix 5380 controller is throwing a Major Fault Type 3 Code 23 every time I try to switch it to Run mode. It happens right after a download or power-up. What should I check first?
A T03:C23 fault on a Logix 5000 controller indicates that a required I/O module connection was not established before the controller entered Run mode, within its configured time limit. This often occurs during the transition from Program to Run, or at power-up if I/O devices take longer to connect than the controller's timeout. The fault is triggered when the 'Major Fault On Controller If Connection Fails While in Run Mode' option is enabled for the module.
Likely causes and checks
1Controller switched to Run too soon
- Points to it
- The controller was commanded to Run mode before all configured I/O modules had established their connections. This is common after a program download or a mode change.
- Check
- Observe the controller's I/O status indicator. Ensure it is solid green, indicating all I/O connections are established, before switching the controller to Run mode.
2Remote I/O powers up slower than the controller
- Points to it
- If remote I/O racks or network devices take longer to power up and establish connections than the controller's internal time limit, the controller will fault when it attempts to enter Run mode.
- Check
- Compare the power-up sequence and connection times of your remote I/O racks and network devices against the controller's configured connection time limit (e.g., 30s for non-redundant 5380/5580 controllers).
3Missing or non-connecting required module
- Points to it
- A specific I/O module that is configured as 'required' is either physically missing, incorrectly keyed, or has a persistent issue preventing it from establishing a connection.
- Check
- Identify the module that consistently fails to connect. Verify its physical presence, correct keying, and inspect its network path and configuration within the 'Connection' tab of its properties in Studio 5000 Logix Designer.
Next check: After checking the I/O indicator and ensuring all modules are online before switching to Run, if the fault persists, verify the power-up timing of your remote I/O. If a specific module consistently fails to connect, investigate that module's physical status and network path.
Related questions
Describe the fault or upload a photo, and InduQT checks it against the manufacturer manuals. Share the result here when it helps someone else.