pulling codes on a Pontiac?

ok my low oil level light has been on since I bought the car lol, I know its a bad sensor because I check the oil level ALL the time so I'm not worried about that.HOWEVER sometimes the check engine light comes on with it. my pop's a damn good mechanic and we can't find anything mechanically wrong with the engine so I think its connected to the low oil level light, but I want to pull the codes to be sure...sooo long story short, can someone tell me how to get the check engine light to flash the codes so I can look them up?

p.s. sorry for the long xplanation