Auto headlights not working properly

I think you are exactly correct. Basically, the way this works is when the ambient light is low it causes the sensor to send a voltage signal that the BCM interprets that voltage as low light and turns on the auto lights.

When the sensor fails the BCM thinks that it is dark, so it keeps the lights on.

I would suggest checking the voltage when the sun is out and then when it is dark. Pull it in and out of the garage and the voltage should change.

Here is a guide that will help with this testing:

https://www.2carpros.com/articles/how-to-check-wiring

If it doesn't change then the sensor is the issue.

Please see the wiring diagram below and let me know what you find.

Thanks