# Was able to upload to ESP32S3 once, but not able to upload anymore **URL:** \ **Category:** Uploading\ **Created:** [November 6, 2025, 10:35am UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666 "2025-11-06T10:35:58Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![yari\_s](https://avatars.discourse-cdn.com/v4/letter/y/dc4da7/32.png) [@yari\_s](https://forum.arduino.cc/u/yari_s)\ **Post date:** [November 6, 2025, 10:35am UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666/1 "2025-11-06T10:35:58Z")
Hello, I created a custom board for the ESP32S3-WROOM-16R8, after fiddling around with the ESP32-S3-DevKitC-1 and getting everything to work. Two days ago I was able to upload code to the board, but now I am unable to and get the error: ```arduino A serial exception error occurred: Write timeout Note: This error originates from pySerial. It is likely not a problem with esptool, but with the hardware connection or drivers. For troubleshooting steps visit: https://docs.espressif.com/projects/esptool/en/latest/troubleshooting.html ``` The way I upload to the board is: 1. Get the board into boot mode with pressing/holding GPIO0 & Pressing/releasing RESET 2. A new COM port appears, so I select that in the IDE 3. Select UPLOAD. The settings used are: USB CDC On Boot: Enabled CPU Frequency: 240MHz Core Debug Level: Debug USB DFU On Boot: Disabled Erase All Flash Before Sketch Upload: Enabled Events Run On: Core 1 Flash Mode: DIO 80MHz Flash Size: 16MB JTAG adapter: Disabled Arduino runs on: Core 1 USB Firmware MSC On Boot: Disabled Partition scheme: 8m with spiffs PSRAM: OPI PSRAM Upload Mode: UART0/HardwareCDC Upload Speed: 115200 USB Mode: Hardware CDC and JTAG Zigbee Mode: Disabled Im pretty sure the connection between the PC and MCU is solid, since the code uploaded on the first day writes over serial and looks as the following: ![WhatsApp Image 2025-11-06 at 09.45.25_900d9afa](https://europe1.discourse-cdn.com/arduino/original/4X/0/7/5/075db7e7b5fd659b4b202af9353803efc0ab0cf5.jpeg) I cannot upload the schematics, but here are some pics: ![image](https://europe1.discourse-cdn.com/arduino/original/4X/6/8/1/68181f03556a71d2fa506ab74cb4df52384a7d44.png) ![image](https://europe1.discourse-cdn.com/arduino/original/4X/d/d/e/dde4fe5532c06cb338c4ab5706bd4e176315275d.png) Also I have tried: 1. A different PC with a clean Arduino IDE install 2. A second (Similar board), Which has the same issue. Able to upload once but not anymore after. 3. The Devkit which has no issues whatsoever I cant seem to figure out what is going on, does anyone have Ideas or dealt with a similar issue? Kind regards, Yari ---
**Author:** ![yari\_s](https://avatars.discourse-cdn.com/v4/letter/y/dc4da7/32.png) [@yari\_s](https://forum.arduino.cc/u/yari_s)\ **Post date:** [November 6, 2025, 10:44am UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666/2 "2025-11-06T10:44:03Z")
@jim-p do you happen to have an Idea? ---
**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\ **Post date:** [November 6, 2025, 11:45am UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666/3 "2025-11-06T11:45:53Z")
> [@yari\_s](#): > > `https://docs.espressif.com/projects/esptool/en/latest/troubleshooting.html` Did you try the troubleshooting steps suggesed in the error message? ---
**Author:** ![yari\_s](https://avatars.discourse-cdn.com/v4/letter/y/dc4da7/32.png) [@yari\_s](https://forum.arduino.cc/u/yari_s)\ **Post date:** [November 6, 2025, 12:49pm UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666/4 "2025-11-06T12:49:47Z")
@jim-p Hello Jim, Yes, I did. the powersupply is a crisp supply at 3.3V with the possibilty to draw 1A. This was checked with the scope. All required GPIO's (for esp32s3 there seem to be different then for esp32) are disconnected. I cannot check if the bootloader is missing, since I am not able to connect to the device. Also I tried erasing flash via esptool.py, but this gives the same error. The Serial port is working, since the code uploaded yesterday talks over the serial. This also indicates that the cable is fine. Kind regards, Yari ---
**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\ **Post date:** [November 6, 2025, 1:38pm UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666/5 "2025-11-06T13:38:38Z")
I think that the Flash Mode should be QIO 80MHz Try a slower download speed (115200) ---
**Author:** ![yari\_s](https://avatars.discourse-cdn.com/v4/letter/y/dc4da7/32.png) [@yari\_s](https://forum.arduino.cc/u/yari_s)\ **Post date:** [November 6, 2025, 1:59pm UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666/6 "2025-11-06T13:59:00Z")
Found the issue! GPIO46 was left floating, this shouldnt be an issue because there is an internal pull down. However when checking there was 1.6v on the pin, if pulled down it uploads! ---
**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\ **Post date:** [November 6, 2025, 2:08pm UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666/7 "2025-11-06T14:08:22Z")
> [@yari\_s](#): > > this shouldnt be an issue because there is an internal pull down. That is true. Can't explain the 1.6V Glad you got it working ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [May 5, 2026, 2:08pm UTC](https://forum.arduino.cc/t/was-able-to-upload-to-esp32s3-once-but-not-able-to-upload-anymore/1412666/8 "2026-05-05T14:08:30Z")
Closed on May 5, 2026, 2:08pm UTC This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.