Frequently asked questions
Modicon M258 stuck in a boot loop after a firmware update?
FAQ000282739
29 July 2026
Question:
A Modicon M258 controller powers up, all LEDs turn on briefly, RUN/MS flashes or turns off, and the Ethernet LEDs continue flashing red/green in a repeating 3-flash cycle. What can cause this boot loop and how can it be recovered?
Answer:
This behaviour could occur if the firmware loaded into the Modicon M258 is not compatible with the controller hardware version.
For M258 PV16 / hardware version 4 controllers, the required firmware depends on the SoMachine version being used:
- SoMachine V3.x: firmware V2.0.31.40
- SoMachine V4.x: firmware V4.0.3.6
Using an incompatible firmware version can cause the controller to reboot continuously and fail to complete startup.
The recommended recovery method is to reload the correct firmware using a USB memory key. Firmware update by USB key is preferred because older versions of Controller Assistant may not check the M258/LMC058 hardware version before downloading firmware. This can allow an incompatible firmware version to be loaded.
After the correct firmware has been reloaded:
1. Reconnect to the controller using the appropriate SoMachine version.
2. Download the correct application.
3. Update the boot application.
4. Power cycle the controller and confirm that the controller starts normally.
If the controller remains in a boot loop after reloading the correct firmware by USB key, and the correct firmware version for the hardware has been confirmed, no further recovery action may be available. In this condition, the controller may be permanently damaged and require replacement.
References:
- For USB firmware reload procedure, refer to Schneider Electric FAQ FA339601.
- For setting the M258/LMC058 to start in RUN mode and updating the boot application, refer to Schneider Electric FAQ FA243994.