Failed to connect to ESP32: Timed out waiting for packet header
What it looks like
Connecting........_____....._____....._____ A fatal error occurred: Failed to connect to ESP32: Timed out waiting for packet header
What it means
esptool got some data from the port but not a valid reply from the bootloader. It is the older wording of the same problem as "No serial data received": the chip is not in download mode, or the link is unreliable.
Likely causes
- The board did not enter download mode.
- Upload speed too high for the cable or USB bridge.
- Another program, such as a serial monitor or a browser tab with the bench open, holding the port.
How to fix it
- Hold BOOT while uploading, then press EN when it finishes.
- Close every serial monitor, including the bench page, before uploading.
- Lower Tools > Upload Speed to 115200.
Paste your full log
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