It comes on 2500 miles after the last reset. 500 miles early of the 3000 mark to give you time to prep for the next change.
To reset it, you just turn the key to on without starting and slowly press the gas pedal to the floor 3 times (not 10 as mentioned), then turn the key off. Start the truck and it should not come back on for 2500 more miles.

The owners manual says it calculates on driving conditions and such. Hogwash. I drive 75% highway miles and could actually go the 6000K as recommended in the woners manual, but every 2500K, there it is. Wife's Caliber is the same way and she drives 95% city, still comes on every 2500K.

 

Thats interesting, great info to know. My old truck (95 4Runner) had no such light so i always went with the 3,000 mile rule (and also checked oil condition every once in a while) So i'm probably not gonna rely on a little light, just go by what the window sticker says and how it looks. I was raised in a family of mechanics so i know my way around my truck pretty well