Introduction
The Allen-Bradley MicroLogix 1400 PLC is a widely used controller in industrial automation, known for its reliability and flexibility in handling small to mid-sized control applications. Like any PLC, it uses error codes to help technicians quickly identify and resolve faults that may occur during operation. However, not all error codes point to actual problems. One of the most frequently misunderstood is error code 0000h. Many users mistake it for a fault, when in fact it means the opposite. This blog explains what error code 0000h really indicates, clears up common misunderstandings, and guides you on proper troubleshooting steps.
Detailed Explanation
In the MicroLogix 1400, error code 0000h is actually a positive sign—it means the controller has no active faults. The “h” at the end shows that the number is written in hexadecimal format, a base-16 numbering system commonly used in electronics and automation diagnostics. In simple terms, 0000h is just the hexadecimal version of zero, and seeing it on the display confirms that the PLC is in a fault-free state.
This code is most often viewed on the PLC’s built-in LCD screen. By navigating to the Advanced Set menu and selecting the Fault Code option, you’ll see 0000h displayed whenever no system errors are present. It is essentially the MicroLogix 1400’s way of saying everything is working normally.
That said, many technicians get confused when they see 0000h while the overall system still isn’t operating as expected. This can happen because the issue may not be with the PLC itself, but with external devices, wiring, or communication links connected to it. Understanding that 0000h points to a healthy controller helps narrow down the search, saving time and preventing unnecessary adjustments to the PLC’s hardware or program.
Common Contexts and Misunderstandings
Although 0000h means the PLC is healthy, it can still appear in situations where the system is not functioning as expected, leading to unnecessary confusion. For instance, users may encounter this code when communication with an HMI or connected drives is lost. Because the PLC itself is not reporting an error, the issue is often external—perhaps due to faulty cabling, incorrect network configuration, or device setup errors.
Another common scenario is after replacing a device or restoring hardware. If the PLC program has been lost or corrupted during the process, the controller may still display 0000h because internally it has no system fault. However, the system will obviously not function as intended until the program is properly reloaded.
System wiring problems or incorrect configuration of external devices can also cause disruptions, while the MicroLogix 1400 itself remains unaffected. In such cases, the 0000h code reinforces that the controller hardware is fine, and troubleshooting efforts should move outward to the connected components.
Some technicians try to clear confusion by cycling the PLC between modes—switching from Run to Program and back to Run. While this may reset LEDs, it does not resolve the underlying external issue.
How to Verify Error Code on MicroLogix 1400
Checking an error code on the Allen Bradley MicroLogix 1400 is a simple process, thanks to the controller’s built-in LCD screen and keypad. To begin, use the navigation buttons to enter the Advanced Set menu. From there, scroll until you find the Fault Code option. If the display shows 0000h, it confirms that the PLC has no active internal fault, which is essentially the controller’s “all clear” signal.
However, problems can still appear even when 0000h is displayed. For example, if the PLC feels unresponsive or the overall system isn’t performing correctly, this usually points to issues outside of the controller itself. In such cases, start by reviewing communication links. Check that Ethernet or serial connections are properly set up, cables are secure, and network settings are correct. Also, make sure that HMIs, drives, or sensors connected to the PLC are configured properly and are exchanging data as expected.
If the fault LED remains on despite the 0000h code, the issue may be related to the PLC program. Confirm that the correct application has been downloaded and is running. In some situations, reloading or verifying the ladder logic in RSLogix 500 can resolve the problem.
In short, 0000h means the PLC itself is fine. If issues continue, focus your troubleshooting on wiring, connected devices, and program integrity.
Conclusion
Error code 0000h in the MicroLogix 1400 is not a sign of trouble—it simply means the controller has no internal faults. The confusion arises when system problems exist even though the PLC reports this code. In those cases, the problem usually lies with communication links, external devices, or missing programs rather than the PLC itself. The key is to confirm the 0000h code through the LCD menu and then shift your troubleshooting outward. By understanding what this code represents, technicians can save time, avoid misdiagnosis, and keep their automation systems running smoothly.
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