On Led = Outputs; Off/Err Led = Error - Omron G9SR Series Operation Manual

Operation manual
8.4.4 ON LED
Color: Green
ON when the outputs are ON.
OFF when the outputs are OFF.
8.4.5

OFF/ERR LED = Error

Color: Red
ON when
FLASH when an error occurs.
Fast blinking & RES or COM fast blinking
= Communication error of another unit
Slow blinking & RES or COM slow blinking
= Communication error of this unit
OFF when all internal diagnostics are successfully passed and OSSD are ON.
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= Outputs
OSSDs are OFF
System startup internal testing failed
G9SR