View source for Raspberry Pi 4/400 Flash Codes

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|shortDescription=The green (ACT) LED on a Raspberry Pi 4 and 400 can indicate what's causing boot problems.
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If you're having trouble with your Raspberry Pi 4 or 400 not booting, usually the culprit is a bad power supply or problems with the SD card or image. If you've confirmed that the power supply is good and it's not even showing the usual power-on screen, check to see if the green LED is flashing - it could be giving you a hint as to what the problem is.

From [https://forums.raspberrypi.com/viewtopic.php?t=58151 the Raspberry Pi forums]
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If a Pi fails to boot for some reason, or has to shut down, in many cases an LED will be flashed a specific number of times to indicate what happened. The LED will blink for a number of long flashes (0 or more), then short flashes, to indicate the exact status. In most cases, the pattern will repeat after a 2 second gap.
<pre>
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
4		4		Unsupported board type
4		5		Fatal firmware error
4		6		Power failure type A
4		7		Power failure type B
</pre>
so:
*if the ACT LED blinks in a regular four blink pattern, it cannot find bootcode (start.elf)
*if the ACT LED blinks in an irregular pattern then booting has started.
*if the ACT LED doesn't blink, then the EEPROM code might be corrupted, try again without anything connected to make sure.
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At least one of these flash codes (SDRAM failure) means your Pi has a hardware fault and you should get it exchanged if it's still under warranty.

Earlier Raspberry Pi models also have flash codes. Check out [https://forums.raspberrypi.com/viewtopic.php?t=58151 the Raspberry Pi forums] for more information.