OMRON CJ1 Series Error Code Analysis: Deciphering the Messages Your PLC is Sending

As an ikwoco engineer specializing in OMRON industrial automation products, I've seen my fair share of perplexing scenarios in the field. One area that often causes confusion, especially among new engineers and technicians, is interpreting the error codes from OMRON's CJ1 Series PLCs. Let’s dive into what these codes mean and how to effectively troubleshoot them.

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Understanding the Basics of OMRON CJ1 Series Error Codes

The OMRON CJ1 Series PLCs are designed with robust self-diagnostic capabilities. When an issue arises, the PLC generates an error code, a specific sequence of numbers and/or letters indicating the nature of the problem. These codes are invaluable for quick and effective troubleshooting.

The Importance of Error Codes

Error codes serve as the PLC’s way of communicating specific issues to the user. They guide you towards the root of the problem, drastically cutting down the time it would take to troubleshoot issues blindly.

Common Error Categories

  • System Errors: Indicate fundamental issues with the PLC’s operation, such as memory or battery failures.
  • I/O Errors: Related to input/output operations, including issues with wiring or connected devices.
  • Communication Errors: Point to problems in data exchange between the PLC and other devices.

Decoding and Addressing Specific Error Codes

Let’s break down some common error codes and their meanings:

Memory Errors (e.g., Error Code 80F1)

This indicates a problem with the PLC’s memory. A checksum error in the user program memory, for instance, could trigger this error. The fix might involve reprogramming or, in extreme cases, replacing the memory unit.

I/O Bus Errors (e.g., Error Codes 80C0 to 80CF)

These errors are often due to issues in the bus line between the CPU and I/O units. Ensuring proper connections and checking for damaged cables or units is a good starting point for resolution.

CPU Fatal Errors (e.g., Error Code 80E0)

A fatal error can halt the operation of the CPU unit. This might be due to programming errors, excessive cycle times, or hardware malfunctions. Immediate attention is required to identify and rectify the root cause.

User-Defined Errors (e.g., Error Codes 4101 to 42FF for FAL(006) Errors)

These are custom errors defined by the user within the PLC program. They are triggered under conditions set by specific instructions in the program, providing a high level of customization in monitoring system performance.

Steps for Effective Troubleshooting

  1. Identify the Error Code: The first step is to ascertain the specific error code displayed by the PLC. This can be done via the PLC’s display panel or a connected programming device.
  2. Refer to the Manual: Consult the OMRON CJ1 Series operation manual to understand the specifics of the error code.
  3. Inspect Physical Components: For errors related to hardware, such as I/O errors, inspect all physical connections, wiring, and components for signs of damage or misconfiguration.
  4. Review the Program: For system and user-defined errors, review the PLC program for potential issues. Look for incorrect instructions, logic errors, or configuration issues.
  5. Reset or Recalibrate: Sometimes, simply resetting the PLC or recalibrating certain settings can resolve the error.
  6. Replace Faulty Components: If a hardware component is identified as the cause, replacing it might be necessary.
  7. Seek Expert Help: If the issue persists, consulting with an OMRON expert or reaching out to technical support is advisable.


Understanding OMRON CJ1 Series error codes is crucial for maintaining the efficiency and reliability of your automation system. By following a systematic approach to decipher these codes, you can significantly reduce downtime and enhance productivity in your industrial operations. Always remember, the error code is not just a warning; it’s a guide towards a solution.

If you’re in need of immediate technical support or are looking to purchase genuine OMRON industrial automation products, feel free to contact us at With over 30 million worth of product inventory, our team at ikwoco is dedicated to providing quick quotations, delivery, and technical support for OMRON products.

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