Teensy 4.1 will not start/boot without USB


New member
I have a teensy 4.1 connected to 4 gas sensors (with their own 12V power supply, a prht sensor (pressure, relative humidity and temp) and it sends serial data via ethernet connection. The teensy is powered through 5V dc-dc converter to Vin, but the teensy will not start/boot unless usb is connected, it is enough with 1sec of usb connection, and then the usb can be disconnected and it will continue to run on Vin, why does it not start/boot without the usb connected? I have now tried to connect two 5V dc-dc converters to Vin, one with 3W and one with 6W capacity and the powersource is 24V 1A (24W) to the dc-dc converters... Can the problem be solved with boot configuration or startup code? Any other ideas?
Sounds potentially like one of the standard things:

Look in your code, typically in setup that looks like:
while (!Serial) {}
while (!Serial) ;
That says wait forever until USB Serial is ready...

If I want to make sure that some stuff I print out early shows up, I usually do it something like:
while (!Serial && millis() < 5000) {} // wait up to 5 seconds for serial to be available