Safety CPU Boot Failure / No Program Loaded
ABB · AC500
What does No program on the controller! mean?
The safety CPU fails to enter RUN mode after power-on, with the DIAG LED on and no boot project loaded. This often occurs if the power-off to power-on pause is less than 1.5 seconds, triggering a power dip detection that prevents the existing boot project from loading.
Common Causes
- Insufficient power-off duration (less than 1.5 seconds) between power cycles, preventing proper CPU initialization and project loading.
- Absence of a valid boot project stored in the safety CPU's non-volatile memory (e.g., due to failed download or memory corruption).
- Defective or improperly seated memory card (e.g., SD card) if used for boot project storage.
- Internal hardware fault in the safety CPU preventing it from booting up the operating system or loading the application.
Repair Steps & Checklist
Click steps to track your progress.
- 1
Power off the safety CPU completely (remove 24VDC supply) and wait for a minimum of 5 seconds before re-applying power.
- 2
Download the complete safety PLC project, including the boot-up parameters, to the safety CPU.
- 3
Verify the integrity and correct insertion of the memory card (if applicable) into the CPU's slot.
- 4
Check the CPU's diagnostic buffer via the PLC programming software for specific boot-related error messages.
- 5
If the issue persists, replace the safety CPU module with a new, programmed unit.