Wrong Bootloader / Upload Timeout
Arduino Microcontroller Board
Severity: ModerateWhat Does This Error Mean?
If uploads timeout on an Arduino Nano clone, the board likely has the old bootloader. Select Tools > Processor > ATmega328P (Old Bootloader) in the Arduino IDE. This changes the upload baud rate to match the older bootloader.
Affected Models
- Arduino Nano (clones)
- Arduino Uno (clones)
- Cheap Arduino-compatible boards
Common Causes
- Nano clone using old bootloader but IDE set to new bootloader
- Board and IDE baud rate mismatch
- Bootloader corrupted or missing
- Wrong board selected in the IDE
How to Fix It
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For Nano clones: select ATmega328P (Old Bootloader).
Tools > Processor > ATmega328P (Old Bootloader). Most cheap Nano clones use the old bootloader.
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Make sure the correct board is selected.
Tools > Board > select your exact board model. Uno, Nano, and Mega use different upload protocols.
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If the bootloader is corrupted: burn a new one.
You need another Arduino or an ISP programmer. Tools > Burn Bootloader with the correct board connected via ICSP.
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Try pressing the reset button just before upload starts.
On some clones, manual reset timing helps the upload connect.
Frequently Asked Questions
What is the difference between old and new bootloader?
The old bootloader uses 57600 baud for upload. The new one uses 115200 baud. If the IDE and bootloader speeds do not match, uploads fail.
How do I know which bootloader my board has?
Try both settings. If Old Bootloader works, you have the old one. Most genuine Arduino Nanos sold after 2018 use the new bootloader. Most clones use the old one.