"How, exactly, do you erase fault codes."


The fault codes are erased using the scanner that reads them. This can be done at a shop, at AutoZone (since you mentioned that's who read them for you), or you can purchase your own scanner.

I use the Dyno Scanner connected to my Treo cell phone. I like this option because I can read the data while driving, and it will give you realtime horsepower curves (I know... it more of a toy than anything).