A fatal error occurred: Failed to connect to ESP32: No serial data received
What it looks like
esptool.py v4.6 Serial port /dev/ttyUSB0 Connecting...................................... A fatal error occurred: Failed to connect to ESP32: No serial data received. For troubleshooting steps visit: https://docs.espressif.com/projects/esptool/en/latest/troubleshooting.html
What it means
esptool opened the serial port but the chip never answered. The board did not enter download mode, so the bootloader never listened.
Likely causes
- The board's auto-reset circuit did not put it in download mode. Common on some cheap boards.
- A long, thin or worn USB cable that drops data or lets the voltage sag while the chip resets.
- A part on GPIO 0, GPIO 2 or GPIO 12 holding a strapping pin the wrong way.
How to fix it
- Hold BOOT, press and release EN or RST, then release BOOT and upload again. Or hold BOOT while "Connecting..." is printed.
- Try another USB cable that you know carries data.
- Lower Tools > Upload Speed to 115200.
- Disconnect parts from the strapping pins and try again.
- Put a 10 µF capacitor between EN and GND if your board never enters download mode by itself.
Paste your full log
The lines around the error usually say more. Paste everything from the reset to the backtrace and the crash translator explains each part. It runs in your browser; nothing is sent anywhere.