Troubleshooting
Organized by symptom, not by product. Start with what you can observe, work through what to check first, and narrow it down without guessing.
Written guides in this section
Full references, procedures, and diagnostic guides published under Troubleshooting.
Processor Faulted
A PLC with its fault light on and no logic running. How to read what it is telling you, the causes in order of likelihood, and how to restart it without repeating the fault.
8 min readUpdated Sep 5, 2026
Outputs Not Energizing
The program says the output is on and the equipment is not running. Where the signal gets lost between the output image and the field device, and how to find the point in a few measurements.
8 min readUpdated Sep 5, 2026
Inputs Not Reading
A switch closes in the field and the program never sees it. How the wetting voltage, the common, sinking and sourcing, and the wiring each lose the signal, and how to find which one did.
8 min readUpdated Sep 5, 2026
Logic Not Executing As Expected
The rung looks right and the plant does something else. The scan-order, duplicate-output, unscheduled-routine, and data-type traps behind it, and how to find which one you are in.
8 min readUpdated Sep 5, 2026
Program Will Not Download
The software refuses to download, or the download starts and fails. The version, path, mode, memory, and protection problems behind it, and the order to check them in.
7 min readUpdated Sep 5, 2026
Retentive Data Lost
The plant came back from a power cycle with zero setpoints, zero totals, and the wrong pump as lead. Which backup failed, which restore overwrote what, and how to get the data back and keep it.
7 min readUpdated Sep 5, 2026
Browse Troubleshooting
PLC
PLC Troubleshooting in industrial control systems — covering 6 topic areas in the CurryControls.com controls and automation knowledge hub.
6 topics
SCADA
SCADA Troubleshooting in industrial control systems — covering 6 topic areas in the CurryControls.com controls and automation knowledge hub.
6 topics
Instrumentation
Instrumentation Troubleshooting in industrial control systems — covering 6 topic areas in the CurryControls.com controls and automation knowledge hub.
6 topics
Communications
Communications Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
5 topics
Networks
Network Troubleshooting in industrial control systems — covering 6 topic areas in the CurryControls.com controls and automation knowledge hub.
6 topics
Control Panels
Control Panel Troubleshooting in industrial control systems — covering 6 topic areas in the CurryControls.com controls and automation knowledge hub.
6 topics
VFDs
VFD Troubleshooting in industrial control systems — covering 6 topic areas in the CurryControls.com controls and automation knowledge hub.
6 topics
Pumps
Pump Troubleshooting in industrial control systems — covering 6 topic areas in the CurryControls.com controls and automation knowledge hub.
6 topics
Valves
Valve Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
5 topics
Radio
Radio Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
5 topics
Fiber
Fiber Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
5 topics
Cellular
Cellular Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
5 topics
Power
Power Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
5 topics
Grounding
Grounding Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
5 topics
Noise & Interference
Noise & Interference in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
5 topics
Direct contact
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References to manufacturers, products, model numbers, software platforms, technical specifications, companies, standards organizations, or other organizations are provided for informational purposes and do not imply sponsorship, endorsement, authorization, or affiliation unless expressly stated. Manufacturer specifications must be independently verified against current manufacturer documentation.