Successfully Added
The product is added to your quote.
2 Year Warranty on ALL products
When Automation Communication Fails: How to Diagnose PLC, Drive, and HMI Network Issues
Few problems bring production to a halt faster than a communication failure. When PLCs lose I/O, drives drop offline, or HMIs stop updating, the system may still be powered—but it’s effectively blind. These failures often look complex, but in reality, most communication issues fall into a handful of predictable categories.
This guide walks through the most common causes of industrial automation communication failures, how to diagnose them efficiently, and which components are most often involved—so you can restore control without unnecessary part swapping or guesswork.
What a Communication Failure Really Looks Like
Communication issues don’t always trigger a clear “network error.” Instead, they often appear as symptoms such as:
- PLC faulting or switching to stop mode unexpectedly
- Drives showing “no comms,” “fieldbus error,” or reverting to local control
- HMIs freezing, displaying stale data, or losing tag updates
- I/O modules intermittently dropping in and out
Because power is still present, teams often assume the controller or drive has failed—when the real issue is the communication path between devices.
The Most Common Root Causes
1) Loose, damaged, or misrouted network cabling
Industrial networks live in harsh environments. Vibration, temperature swings, and cabinet crowding take a toll over time. Ethernet cables routed alongside high-power motor leads are especially vulnerable to noise and intermittent signal loss.
If a problem disappears when equipment is stationary—or only occurs during motion or startup—physical cabling is one of the first places to look.
2) Power supply instability affecting communication modules
Network cards, PLC CPUs, and remote I/O all rely on stable control power. Even brief voltage dips can cause communication modules to reset while the rest of the system appears “alive.”
Upgrading or validating control power is often overlooked during troubleshooting, yet it is a frequent root cause. Plants using Siemens platforms, for example, commonly rely on regulated control power to maintain stable communication:
Siemens Power Supplies & Accessories
3) Network overload or poor segmentation
As systems expand, it’s common for multiple HMIs, drives, PLCs, and diagnostics tools to share a single network. Excessive traffic, broadcast storms, or unmanaged switches can introduce delays or dropped packets—especially in real-time control applications.
If communication issues worsen after adding new devices, software, or remote access tools, network load should be evaluated immediately.
4) Mismatched firmware, protocols, or configuration
Communication failures often appear after maintenance or upgrades. Replacing a drive, PLC, or HMI with a similar—but not identical—model can introduce subtle incompatibilities:
- Different protocol versions
- Unsupported firmware combinations
- Incorrect node addressing or device names
This is especially common with legacy PLCs or discontinued drive families where documentation may be limited.
High-Risk Components in Communication Failures
While cables and switches are frequent culprits, certain automation components are more likely to surface communication problems when something goes wrong.
PLCs and Remote I/O
The PLC is the traffic coordinator of the system. A single faulty communication port or I/O adapter can make it appear as though multiple field devices are failing at once.
Common platforms involved in these scenarios include:
Siemens SIMATIC Controllers
Siemens S7-300 PLCs
Drives with Fieldbus or Ethernet Control
Modern drives depend heavily on network communication for speed reference, feedback, and diagnostics. When communication drops, many drives default to fault states or safe stop conditions.
Drive families commonly affected include:
ABB Variable Frequency Drives
Toshiba Industrial Drives
HMIs and Operator Interfaces
HMIs are often blamed first because they are the most visible failure point. In reality, they are usually the messenger—showing the effects of a deeper communication issue upstream.
If HMIs lose tags or freeze intermittently, the underlying PLC or network stability should be checked before replacing the screen.
Example operator interface platforms include:
Industrial HMI Panels & Touchscreens
A Step-by-Step Way to Troubleshoot Communication Issues
Instead of chasing symptoms, use a structured approach:
- Confirm whether the issue affects one device or the entire network
- Check control power stability first
- Inspect physical cabling and terminations
- Verify addressing, firmware, and protocol settings
- Substitute a known-good communication module or cable if available
This process isolates the problem faster and prevents unnecessary replacement of expensive components.
Why Having the Right Spares Matters
Communication failures are difficult to diagnose under pressure. Having a known-good PLC CPU, communication card, power supply, or drive interface available can cut recovery time dramatically.
That’s why many maintenance teams keep tested spares for high-risk components rather than waiting for an emergency order.
How Industrial Automation Co. Supports Faster Recovery
Industrial Automation Co. helps maintenance and engineering teams source reliable PLCs, drives, HMIs, and power components—especially for legacy and hard-to-find platforms. When communication issues point to a failing module or interface, having the correct replacement on hand makes the difference between hours of downtime and days.
Contact Industrial Automation Co. for help identifying and sourcing the right automation components