In Siemens S7 300 CPUs, there is a series of LED lights with different colors which shows us the modes, status, and errors of the PLC.
S7 300 LED Errors
SF
System fault: it indicates there is an error in the system, this error could be software error like an error in programming or hardware error like a power loss of one of the input modules
Color: Steady Red
BF
Bus Fault: it indicates that there is an error in the system network, like a bad contact in one of the communication connectors, or there is an overlap between the addresses in the network
Color: Steady Red
MAINT
Maintenance: where ever this indicator energized this means that the CPU is not working anymore and needs a service, but this is rarely happening.
Color: Steady yellow
DC5V
This led indicates that there is a 24 Volt DC provided to the CPU.
Color: Steady Green
FRCE
Force: it indicates that at least one of the PLC inputs or outputs is forced to on or off.
Color: Steady yellow
Run
Run mode is on whenever the CPU is working properly without any troubles, and flashes in the startup of the CPU.
Color: Steady Green
STOP
a.
When the CPU is in STOP mode or there is a software/hardware error.
Color: Steady yellow
b.
For a memory reset request when inserting the memory card.
Color: Yellow flashes slowly
c.
When the memory reset is being carried out.
Color: Yellow flashes quickly
Author: Karim Ali Anwar
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Hello Karim, thank you very much for your explanation about the S7 300. Have a great day.