A consolidated reference for the Rockwell CompactLogix major and minor fault types you are most likely to hit, with the common remote-checkable cause for each and the log to read before you consider swapping the controller.
CompactLogix surfaces a fault through the controller properties in Studio 5000 (the fault log) and the OK/FAULT LEDs on the module. Logix faults are typed by a major type code (00–99) and a code that identifies the exact instruction or condition. Reading type + code together is how a remote specialist isolates the problem.
| Fault source | Where you see it | What it tells you |
|---|---|---|
| Fault log | Controller Properties > Fault in Studio 5000 | The type and code plus the module/instruction that raised it |
| LED state | Controller OK/FAULT LEDs | RUN/FAULT mode and a quick health read |
| I/O module status | Controller Organizer | Which configured module is in fault and its condition |
The table lists the most common major fault types, their meaning, and the first remote check. Likelihood reflects field frequency.
| Type | Meaning | Likelihood | First Remote Check |
|---|---|---|---|
| Type 01 | Programming or instruction error | Med | Read the fault code in the log; it names the rung or instruction that faulted |
| Type 02 | Programming or instruction error (explicit) | Low–Med | Check the instruction that raised the code and the operands it uses |
| Type 03 | I/O fault — a configured input/output module errored | Med–High | Expand the I/O tree and read the faulted module's status; check power and connection |
| Type 07 | CPU / firmware fault on the controller | Low | Note the code and cycle the controller; confirm firmware revision before deciding |
| Type 15 | Communication fault — a partner or bridge unreachable | Med | Confirm the partner's IP/connection and the network path to the module |
| Watchdog (Type 4x/50) | Controller watchdog or task timing fault | Low | Review the task scan time and the program that exceeds the watchdog |
The type narrows the family; the code names the exact instruction or module. Both are needed, and both live in the fault log you can export remotely.
Work through these in order. Each step is something you can perform and report back on without opening the panel or removing parts.
Open Controller Properties > Fault in Studio 5000 and note the type, code and the module/instruction. This is the single most useful artefact for remote triage.
Note the controller OK/FAULT LEDs and the status of any faulted I/O module in the organizer. LED + module status + log tells the story.
Was there a download, a module added/replaced, a firmware update, or a wiring change right before? Recent changes usually reveal the trigger.
Confirm the online project matches the offline version and the module firmware is compatible. A config/firmware mismatch is a common one-shot fault trigger.
After clearing the cause, clear the fault and run the controller and the faulted I/O to confirm a sustained healthy scan.
A CompactLogix fault is an I/O, programming or communication path more often than a controller hardware failure. Cross-reference the specific conditions: Major fault · Watchdog stop · All controller symptoms · PLC technology.
In remote practice, most CompactLogix faults are resolved from the fault code, the program logic and the I/O mapping — not by replacing the controller. Escalate to a specialist when a major fault points to a damaged backplane or module, when the controller repeatedly faults in the same program step and a full download does not clear it, or when the line is down and correct diagnosis matters more than fast guesses.
To get the fastest accurate read, send these three things. All are read from the controller or RSLogix / Studio 5000 — no hardware removal.
Send these and we can usually confirm whether the fault is remote-resolvable before you book any hands-on visit. machinery controller troubleshooting guidance
A major fault stops controller execution. It is identified by a type code (01 programming, 03 I/O, 07 CPU, 15 communication, etc.) and a code that pinpoints the instruction or module. The fault log in Studio 5000 provides the detail.
Type 03 is an I/O fault — a configured module errored. The code names the module and condition; it is commonly a module power, connection or firmware issue that is remotely-checkable.
Yes. Share the fault log, module status and what changed; a specialist interprets the code and guides recovery. We never take control of your controller.
A fault that reproduces in the same rung usually points to a logic or data problem rather than hardware — a division by zero, an array index out of range, a bad tag reference, or an unrecoverable instruction fault. Read the fault code and the exact rung from Studio 5000; a specialist can walk through the instruction semantics remotely.
Send us the error code, a photo of the screen and what you already tried — an independent specialist reviews your case and replies with an evaluation, typically within 24 hours.
Submit Your CaseSend the fault log, LED state and what changed. We interpret it and guide recovery remotely — no controller swap unless it is genuinely required.
Submit Your Case Connect With SpecialistsWe do not perform hardware repair, we do not replace parts, and we cannot promise a 100% resolution. Our role is limited to remote diagnostic and step-by-step guidance based on the information, photos and logs you share.
Before changing drive parameters or replacing parts, verify against the official documentation from Rockwell Automation:
Tip: for simple issues, a general-purpose AI assistant can help you interpret a fault code — but always cross-check any corrective action against the official manual before applying it.
The most common controller trip path in detail.
When a task exceeds the watchdog timer.
A related PLC fault reference for another vendor.
Full controller troubleshooting collection.
Part of the full library: fault codes by brand — ACS580, S7-1200, ATV320, Sigma-7, CompactLogix, FX5U, VF-2, Robodrill and CFW800.