On a Raspberry Pi 4, the green “ACT” LED indicates boot errors using certain blinking patterns. The following table shows what the different patterns mean (source of the table is the official documentation).
Hint: In case your LED does not flash, or turns completely of after some flickering, your EEPROM bootloader might be corrupt. In that case, you can recover it by flashing the bootloader to an SD card using the Raspberry Pi Imager. Just select Choose OS –> Misc utility images –> Bootloader (for your version) –> desired boot mode (e.g. SD). Then insert the SD card into the Pi after flashing and wait several seconds. This should fix the bootloader.
| Long flashes | Short flashes | Status |
|---|---|---|
| 0 | 3 | Generic failure to boot |
| 0 | 4 | start*.elf not found |
| 0 | 7 | Kernel image not found |
| 0 | 8 | SDRAM failure |
| 0 | 9 | Insufficient SDRAM |
| 0 | 10 | In HALT state |
| 2 | 1 | Partition not FAT |
| 2 | 2 | Failed to read from partition |
| 2 | 3 | Extended partition not FAT |
| 2 | 4 | File signature/hash mismatch – Pi 4 |
| 3 | 1 | SPI EEPROM error – Pi 4 |
| 3 | 2 | SPI EEPROM is write protected – Pi 4 |
| 3 | 3 | I2C error – Pi 4 |
| 3 | 4 | Secure-boot configuration is not valid |
| 4 | 3 | RP1 not found |
| 4 | 4 | Unsupported board type |
| 4 | 5 | Fatal firmware error |
| 4 | 6 | Power failure type A |
| 4 | 7 | Power failure type B |