Mitsubishi MELSEC L Series User Manual page 97

(2) Using a programming tool
The error details and cause can be checked by connecting a programming tool to the CPU module.
If the connection cannot be established, check that the settings in the programming tool are correct.
Operating manual for the programming tool used
(a) PLC diagnostics
When the ERR.LED turns on or flashes, check the error in the PLC diagnostics of the programming tool and
eliminate the error cause.
[Diagnostics]
For details on the PLC diagnostics, refer to the following.
Operating manual for the programming tool used
[PLC Diagnostics...]
CHAPTER 15 TROUBLESHOOTING
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