Originally Posted by Rosewood
what happens if you reset it without changing the oil. not that i would do that, but it would be nice to know it it is testing the oil or just working off of mileage
It's working off of mileage and how the vehicle has been driven. It isn't a pure mileage counter; it notices how far you drive it each time and the manner of your driving, then selects a maintenance schedule to use, reminding you as you come up on the appropriate mileage.
If you reset it without doing an oil change, it will assume you have done so. There have been extremely few vehicles that use sensors to check the oil itself in order to trigger the reminder- it's a much more expensive way to do it and you aren't really talking a huge difference in the final result anyway.