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What does the Red LED labeled ERR blinking or flashing on the M241 PLC mean?

Published date: 26 November 2018


The Red LED labeled ERR is blinking/flashing on M241 series PLC. What does it mean?

Product Line
SoMachine v4.1+, 

M241 PLC (TM241C24R, TM241C24T, TM241C24U, TM241C40R, TM241C40T, TM241C40U, TM241CE24R, TM241CE24T, TM241CE24U, TM241CE40R, TM241CE40T, TM241CE40U, TM241CEC24R, TM241CEC24T, TM241CEC24U)


M241 LED physical indicator light


There are three types of ERR LED blinking:

Regular flash -

The LED turns on for 500ms and then off for 500ms regularly.

This signifies an INVALID_OS controller state There is not a valid firmware file present in the flash memory. The controller does not execute the application. Refer to the Firmware Upgrade section of the SoMachine HTML Help to restore a correct state.


Single flash -

The LED turns on for 1000ms, then off for a short 200ms and repeats this pattern.

This signifies an EMPTY controller state, no program has been loaded to the PLC in this state (usually after a Firmware Upgrade procedure has been done or when a Reset Origin is performed)


Fast flash -

The LED flashes on and off alternating quickly within 500ms at a regular pace.

This signifies an EMPTY after a system error detected controller state.

This state is the same as the normal EMPTY state. But the application is present (as a BOOT project), and is intentionally not loaded into working memory. A next reboot (power cycle), or a new application download, will restore correct state.


For more information, please refer to the SoMachine HTML Help in the section:

Logic Controllers -> M241 Logic Controller -> Programming Guide -> Controller States and Behaviors -> Controller States Description

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