Most rain sensors rely on using infrared light being sent out of the sensor, the light hits the water and is refracted instead of being directly reflected back to the sensor. When the sensor doesn’t see the usual levels of light coming back it turns on the wipers. The less it sees its infrared light coming back the faster the wipers go. I don’t think water movement comes into play unless the Ascent has a different type of rain sensor.
Being in the hot and humid south and having water condensate on my windshield every night so I am used to your suggestion #3. I do think it would be rather nice if the auto wipers would be active from the start.
Just so everyone knows this is a very minor issue to me and not the end of the world. I would like it to kick in right away but I am not that fussed about it. I also wonder if this is common across all cars with rain sensing wipers because I never owned a car with this feature before. I am more curious about why the delay happens then anything.
Alas, I think you misunderstood, through fault of my own for not going into more detail. Sorry about that.
With the water not moving and the car off, the system calibrated when turned on. It's always doing so. There are no usual levels of light. That's how it works day and night.
So, the system does not realize that it is seeing reflected water because there's no change in what it detects. It's changes in reflections it detects, not specifically/solely reflections.
That's also why going around a curve at just the right time of day causes the sun to refract through the windshield onto the sensor and trigger the system.
The sensor can also be set off by hand, btw.
