The secondary air pump simulator...simulates increased o2 flow trough your o2 sensor (simulating a blowing pump) for the first 30 seconds after starting the car only in cold weather temperature. That is the only time the pump does anything.
then after that time it restores normal o2 sensor input.
so the ecu senses the pump doing it's job and goes on happily ever after
here is a thread I made about it
http://www.zpost.com/forums/showthre...&highlight=sap
You can buy one on ebay or make your own for 25 bucks...it involves connecting a wire to your sap and cutting your o2 sensor to insert dummy data.