Connection lost error

[Dbsimmons]

Bug Report - flash.comma.ai

Device: comma 3/3X
Serial: N/A
Error: LOST_CONNECTION
Step: CONNECTING
Last Message: N/A

OS: Windows 10/11
Sandbox: None detected
Browser: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/145.0.0.0 Safari/537.36
URL: https://flash.comma.ai/
Time: 2026-03-04T18:22:57.000Z

Console Logs

[2026-03-04T18:14:17.246Z] [info] flash.comma.ai version: a240b3a
[2026-03-04T18:14:17.354Z] [info] [ImageManager] Initialized
[2026-03-04T18:22:29.035Z] [info] [Flash] No device selected
[2026-03-04T18:22:49.500Z] [error] [Flash] Connection error {}
[2026-03-04T18:22:49.500Z] [debug] [Flash] error 4

[davidzachariah]

@Dbsimmons , were you able to resolve your issue? I am having similar issue, tried diff computers, cables without success

[Dbsimmons]

@Dbsimmons , were you able to resolve your issue? I am having similar issue, tried diff computers, cables without success

No I am still having the issue

[davidzachariah]

@Dbsimmons Thanks, same here. Failed Flash #188 - Seems resolved it by opening the case and clean-up.

[itsdestin]

Not certain this is the same root cause (this report is Windows), but possibly useful context: we hit this exact signature — LOST_CONNECTION at CONNECTING, console Connection error {} / error 4, failing instantly — on Linux, and traced it to the browser being denied write access to the USB device node (USBDevice.open() throws SecurityError, which the current UI folds into the generic lost-connection screen). #215 splits that case out into its own error with the fix shown on screen, which should make future reports like this one more diagnosable.

@Dbsimmons if your error appeared immediately after selecting the device, the Windows equivalent of this failure is usually the WinUSB driver not being bound (the Zadig step — worth re-running, selecting the QUSB_BULK device and installing WinUSB) or another program holding the device (QPST/QFIL/phone tools — close them or try a fresh boot). If it appeared only after several minutes, it's more likely a genuine connection drop — different cable/port is the right advice there.