# Thonny cannot connect to ESP32 MicroPython: port, firmware and boot mode

> Fix Thonny that cannot find or talk to an ESP32 running MicroPython: choose the interpreter, the right COM port, flash the firmware and use a data cable.

Canonical: https://roboticsengineering.in/fix/thonny-cannot-connect-esp32-micropython/ | Published: 2026-11-03 | Updated: 2026-11-03

**Thonny must be set to the MicroPython (ESP32) interpreter and the right COM port, and the board must have MicroPython firmware flashed.**

## What the message means

A blank ESP32 has no MicroPython on it, so there is no prompt to connect to. The interpreter choice and port also have to match.

## Fix it in this order

1. Use a USB cable that carries data, and check that a COM port appears.
2. In Thonny open Run > Configure interpreter and choose MicroPython (ESP32) and the port.
3. Use the “Install or update MicroPython” option in the same window to flash the firmware if the board is new.
4. If flashing fails, hold the BOOT button while it connects.
5. Press the stop button or Ctrl+C to interrupt a running program.
6. Close other programs that use the same port.

## If you see this, do this

| You see | Do this |
| --- | --- |
| No port in the list | Cable or driver. |
| Port found, no prompt | Firmware missing. Flash it. |

## Related

[failed to connect](https://roboticsengineering.in/fix/esp32-failed-to-connect-timed-out-waiting-for-packet-header/), [USB driver](https://roboticsengineering.in/fix/arduino-nano-clone-not-detected-ch340-driver/).

Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.