Siemens S7 300 CPU Status and LED Errors Explanation

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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