I have the same problem with my 3 months old car. I turn the switch to position 3 (automatic headlamp control) hoping that the light would be off during the day. Today was a quite sunny spring day. I was driving for about 5 hours (from 10am to 3pm) on the interstate and the light never went off.
Felt like a fool.
How can I check if the sensor is faulty? Can I do it with a flashlight placed right on the windshield glass (over the sensor)?