"Secondary air injection" is, I believe, the correct term. It injects air into the exhaust at startup to increase O2 in the exhaust to heat up the cats faster.

EPA nonsense, really. If it does NOT run, the CEL comes on and you get a P401 code. I know this because SO many of our cars experience a fracture of the solder on the RCM such that the pump won't run - and that means you can't pass an emissions test. A few minutes with a 100 watt soldering iron and some rosin core solder fixes it.

Ask me how I know this. (Twice in 70,000 miles)