Mitsubishi FX5U PLC Error Codes and How to Fix Them

How to Fix FX5U Error 2400H

2400H is a module verification error. On an FX5U, it should not be treated as a generic memory error.

Typical causes include:

• An expansion or intelligent function module has no power
• An extension cable is loose or damaged
• The physical module arrangement differs from the project
• A module was added or removed without updating parameters
• Internal bus communication is affected by electrical noise
• An expansion module has failed

Start by opening System Monitor. The affected module or slot will often be visible in the system configuration information.

Power down the control panel before reseating modules or extension cables. Isolate the supply, verify that the circuit is de-energized, and follow the machine manufacturer’s lockout procedure.

Check the module arrangement against the GX Works3 project. Inspect connectors for bent pins, contamination, poor seating, and cable damage.

If the configuration and wiring are correct, disconnect nonessential expansion modules one at a time, where the machine design permits, to isolate the failing component.

When sourcing a replacement through Kwoco, provide the full CPU and module model numbers, existing firmware versions, system configuration, and a screenshot of the GX Works3 diagnostics. Matching only the general product family is not enough.

How to Fix Watchdog Error 2500H

The watchdog timer monitors whether the CPU is completing its processing within the allowed time.

Error 2500H can occur when:

• The initial scan takes longer than the configured execution-monitor time
• A loop takes too long to complete
• An interrupt program runs longer than its execution interval
• Interrupts occur too frequently
• Communication or data-processing routines block program execution
• The watchdog setting is too short for the actual application

Check the maximum scan time and compare it with the execution-monitor setting.

Use Error Jump and program monitoring to identify long loops, repeated communications, excessive table processing, or interrupt routines performing too much work.

Increasing the watchdog setting may prevent the immediate trip, but it should not be used to hide an inefficient or blocked program. First confirm why the scan time increased.

Fixing Program Errors 3100H, 3200H, and 3400H

Error 3100H: Unsupported or Invalid Program

This error indicates that the CPU cannot correctly execute part of the downloaded program.

Use Error Jump to find the reported location. Check for unsupported instructions, invalid instruction combinations, incompatible function blocks, or code created for another CPU type.

Rebuild the entire project after making the correction.

Error 3200H: Assignment Mismatch

This often appears when device or label assignments have been changed, but only the parameters were downloaded.

Write both the parameters and program files together. A partial download can leave the PLC with a program that no longer matches its memory assignment.

Error 3400H: Division by Zero

Inspect the divisor at the reported program step.

Do not simply reset the PLC. Add logic that prevents execution when the divisor is zero or outside the expected operating range. Also check whether the zero value is caused by a disconnected sensor, failed communication, or uninitialized data.