Resolving Omron NJ301-1100 ERROR LED After RUN Flashing

An NJ301-1100 whose RUN LED flashes after power-up and then drops into a steady ERROR LED has finished its startup sequence and found a fault it will not run with. The LEDs do not tell you which fault. You get the cause from the controller's event log in Sysmac Studio. The checks below run in commissioning order. Each one names the reading to take and where each outcome sends you next.

How the NJ301-1100 Startup LED Sequence Works

At power-on the NJ CPU goes through these stages:

• It runs hardware self-diagnostics.
• It loads the user program, Controller configuration and settings from non-volatile memory.
• It checks the physical CJ-series unit configuration on the rack against the project.
• It starts the built-in EtherNet/IP and EtherCAT ports.

RUN flashes while this startup is in progress. The number of flashes you count (ten, three times over) reflects how long startup took. It is not a numeric error code. The NJ reports errors as events in its log, not as blink patterns.

When startup finishes, one of two things happens. With no fault, RUN goes steady in RUN mode or turns off in PROGRAM mode. With a Controller error, the ERROR LED shows the fault level:

POWER	RUN	ERROR	Meaning	Next check
Lit	Off	Steady	Major fault level: the user program is stopped	Check 2 (go online)
Lit	Lit	Steady	Partial fault level: one function unit (for example EtherCAT) has stopped and the program still runs	Check 2
Lit	Lit or off	Flashing	Minor fault level	Check 2
Off or flickering	Any	Any	Supply problem	Check 1

Check 1: POWER LED and Rack Supply

Prerequisite: you have access to the rack with power on.

1. Read the POWER LED on the power supply unit and on the CPU.
   • Steady: go to step 2.
   • Off or flickering: measure the supply input at the power supply unit terminals and compare it with the rating printed on that unit.
2. Watch the POWER LED through a full power cycle.
   • A POWER LED that dips or cycles while RUN is flashing points to a power supply unit that is overloaded or failing. Remove the non-essential CJ units to cut the load, then retest.
3. Confirm the End Cover is fitted on the right-hand end of the rack and every unit is latched with its slider fully locked. A missing End Cover or a loose unit connection stops the NJ at startup with a major fault.

When POWER is steady and the rack is mechanically complete, go to Check 2.

Check 2: Sysmac Studio Online Connection

Prerequisites:

• A PC with Sysmac Studio installed.
• A USB cable for the CPU's peripheral USB port.
• The project file for this machine, if you have one.

Use USB first. A direct USB connection needs no IP configuration, so a corrupted or unknown Ethernet setting cannot block it.

1. Connect the USB cable. In Sysmac Studio, open the project, or create a new one with the device set to NJ301-1100.
2. Select Controller > Communications Setup, choose the direct USB connection, then go online.
   • Online succeeds: go to Check 3.
   • Online fails over USB with POWER steady and ERROR steady: swap the cable and PC USB port, then retry.
   • Still no connection: the CPU cannot complete basic communication. Treat it as a CPU hardware fault and go to the last section.

If the project on the PC differs from what is in the controller, going online still works. Do not transfer anything yet. Read the fault first.

Check 3: Read the Controller Event and Branch on Its Source

1. While online, open Tools > Troubleshooting. Read the Controller Errors tab for active errors.
2. Open the Controller Event Log and note, for the first event logged at the failing power-up:
   • the event code
   • the event name
   • the source
   • the attached information
   The first event is usually the cause. The events after it are often consequences.
3. Branch on the source and content:

Event points to	Mechanism	Action
User program, Controller configuration or settings data (transfer error, data corrupted, data missing)	Non-volatile memory holds an incomplete or damaged project. Typical causes are a download interrupted by power loss or a memory fault. The CPU refuses to execute it.	Clear memory and re-transfer (next section)
Unit configuration or I/O bus (unit missing, wrong model in slot, bus check error)	The physical CJ rack does not match the Unit Configuration in the project, or a unit or its connector has failed.	Correct the rack or the I/O Map in the project. Reseat the units. Isolate the faulty unit by removing units one at a time with power off.
EtherCAT master (slave missing, network configuration mismatch, link down)	A slave is off, miswired, or replaced with a different device or revision than the network configuration expects.	Power and check the slaves, cabling and node addresses. Compare the actual network with the project's EtherCAT configuration.
EtherNet/IP port (IP duplication, settings error)	Port settings conflict with the network or failed to load.	Correct the built-in EtherNet/IP port settings and re-transfer.
Battery or clock	Backup battery is low or missing and clock data was lost.	Replace the battery and set the clock. This alone does not normally stop the program.
CPU hardware (self-diagnosis failure)	Internal fault detected by self-test.	Contact Omron technical support for repair or replacement.

Clearing Memory and Re-transferring the NJ Project

This is the resolving procedure for the most common startup major fault: a corrupted or incomplete user program or configuration.

Prerequisites:

• You hold a known-good project file for this machine.
• The machine is safe to stop.
• You are online over USB.

1. Confirm the CPU is in PROGRAM mode. The status bar in Sysmac Studio shows the operating mode. Change it to PROGRAM if needed.
2. Run Controller > Clear All Memory and confirm the prompt. This removes the damaged program and settings. Wait for the operation to complete before continuing.
3. Cycle power to the rack. With memory cleared, the controller starts with no project. The original startup major fault should not reappear. Any Controller errors still present now come from hardware or the rack configuration, so return to Check 3.
4. Go back online. Run Controller > Synchronize and transfer the project to the controller. Confirm the transfer completes with no errors reported in the output pane.
5. Open the Troubleshooting window and select Reset All to clear any recorded errors.
6. Cycle power again. Some major fault levels clear only after a restart, and the power cycle also proves the project survives startup from non-volatile memory.

For a unit configuration or EtherCAT branch, apply the correction from Check 3. Then run steps 4 to 6 so the controller holds a project that matches the hardware.

Confirming the Controller Reaches RUN

1. Power up and watch the LEDs. RUN should flash through startup, then stay off with the startup mode set to PROGRAM, or go steady with it set to RUN. ERROR must stay off.
2. Go online and open the Troubleshooting window. Controller Errors must show no active events. Check the event log to confirm this power-up logged no new major or partial fault.
3. Switch to RUN mode if the startup mode is PROGRAM. Confirm the RUN LED goes steady.
4. Verify I/O and EtherCAT communication:
   • Watch live values for the CJ units in the I/O Map.
   • Confirm the EtherCAT slaves reach operational state in the EtherCAT configuration view.
5. Cycle power one final time without the PC connected. Confirm the controller comes back to RUN with ERROR off. This proves the fix persists in non-volatile memory rather than depending on the online session.

FAQ