PLC Error Code Lookup
Look up a deliberately small, source-verified set of Siemens S7-1500 and Rockwell Logix connection codes. Unknown model/code pairs are not guessed: the tool routes you to the matching OEM diagnostic record.
Lookup
Quick examples
Quick: one-click fault presets. Advanced: pick brand, code family, and severity filter for field triage.
About this calculator
Maps only source-verified PLC fault codes to their OEM wording and a cautious diagnostic path. It does not assign generic meanings to short hexadecimal values because the same value can mean different things across products and code families. If measurements identify a separate distribution fault, continue at the Protection Calculator hub.
Lookup result
Select a model and enter the exact code—or use a verified example above. Default preview: S7-1500 · 16#2942 (reading an invalid peripheral input).
Engineering disclaimer
This tool provides general fault-code information. Codes and procedures vary by model, firmware, and configuration. For safety-related or production-critical faults, follow lockout/tagout and consult qualified automation engineers or OEM support.
Triage sequence (field method)
Use this order before diving into ladder logic—most downtime clears at layers 1–3.
- Power — PLC and field devices at nominal voltage; no blown fuses or tripped breakers.
- Communication — cables, IP/node settings, switch ports, termination on serial buses.
- I/O — module status LEDs, wiring continuity, sensor/actuator supply.
- Program logic — diagnostic buffer, recent downloads, watchdog and task overload.
When multiple codes appear, preserve the full timeline. The earliest event is useful evidence, but confirm the initiating condition from event relationships and OEM diagnostics before changing the system.
PLC error code list (quick open)
Only codes whose exact meaning has been checked against an OEM source are listed here.
Worked example — invalid peripheral input
Scenario: An S7-1500 diagnostic record contains 16#2942. The Siemens source identifies this as reading an invalid peripheral input; it does not by itself prove a cable or remote-I/O communication failure.
- Record the full diagnostic text, timestamp, CPU operating state, and affected address.
- Find the program instruction that reads that peripheral address.
- Compare the address with the downloaded hardware configuration and actual module layout.
- Use the module and CPU diagnostic buffers to determine why that input is invalid before changing hardware.
Verified OEM source registry
This registry is intentionally narrow. Exact code meanings are published only when the product family and code context have been checked against a primary manufacturer source.
| Product family | Code | OEM wording | Primary source |
|---|---|---|---|
| Siemens S7-1500 | 16#2942 | Reading an invalid peripheral input | Siemens STEP 7 / WinCC V16 Readme |
| Rockwell Logix | 16#0203 | Connection timed out | Rockwell module faults 16#0200–16#02FF |
| Rockwell Logix | 16#0204 | Connection Request Error: connection request timed out | Rockwell module faults 16#0200–16#02FF |
A code from another model, code family, or firmware must be resolved from its complete diagnostic record. A matching hexadecimal number alone is not enough.
PLC Fault Diagnostic Decision Table
Use symptoms to choose the next evidence to collect. A symptom can have several causes, so the table does not declare a root cause.
| Symptom | Possible conditions | Evidence to collect first | Category |
|---|---|---|---|
| CPU fault indicator active; outputs unavailable | CPU not in RUN, controller fault, configuration issue, or supply event | Record CPU state and complete diagnostic buffer before reset or power cycle | System |
| I/O module indicators inactive; channels unavailable | Supply, backplane/bus, configuration, or module condition | Record module diagnostics and measure the specified supplies using the OEM procedure | I/O |
| Remote I/O connection changes state intermittently | Target state, configuration, power, physical link, switching, or traffic condition | Correlate connection-fault timestamps with target and managed-switch diagnostics | Communication |
| Analog channel reports overrange/underrange diagnostic | Signal outside configured range, loop condition, wiring, scaling, or channel configuration | Record raw value and channel diagnostic, then measure the signal with an appropriate test method | I/O |
| Program command is true but field output is inactive | Interlock, forcing, channel/module state, field power, protection, wiring, or actuator condition | Trace command and interlocks, then follow the approved energized/de-energized test procedure | I/O |
| Battery or energy-storage diagnostic active | Service interval, low state, disconnected device, or unsupported/failed component | Identify the exact controller and follow its OEM replacement and backup procedure; do not replace while energized unless explicitly required | Maintenance |
| Watchdog or task-overrun diagnostic | Task execution exceeded its configured limit or was blocked | Preserve task/fault data and recent-change history before modifying watchdog settings | Program |
| 24 V supply varies under operation | Source regulation, dynamic load, wiring/terminal drop, protection event, or measurement issue | Measure voltage and current at source and affected load under the same timestamped condition | Power |
Frequently asked questions
How do I find the error code on my PLC?
Check the HMI alarm list, programming software diagnostic buffer (TIA Portal, Studio 5000, EcoStruxure), or module status LEDs. Note exact hex format—Siemens often uses 16# prefix.
What if my code is not in the database?
Record the exact product, firmware, code family, full code, extended status, diagnostic text, timestamp, and operating state. Use that complete record in the matching OEM manual or vendor support system; do not reuse a partial hexadecimal match from another product.
Should I fix secondary errors first?
Preserve the complete timeline first. The earliest event is useful evidence but is not automatically the root cause; use event relationships, controller/module diagnostics, and the OEM procedure to identify the initiating condition.
Are these steps enough for safety PLC faults?
No—safety-rated faults may require certified personnel and vendor procedures. Do not bypass safety functions to clear alarms.
How does this relate to electrical sizing tools?
Only route to electrical calculations when measurements or the complete diagnostic record identify a supply problem. PLC code lookup does not size breakers, conductors, transformers, or control-power sources.
Where can I learn systematic PLC troubleshooting?
See how to troubleshoot PLC error codes, common PLC errors, and common mistakes.
Guides: PLC error troubleshooting · Common PLC errors · Common mistakes