How many codes are you allowed on a 1999 chevy s10 with 2.2 motor

Right , no codes can be present , but the computer has monitors and they will check those , the monitors have to " clear " after a certain amount of driving , each one needs different conditions and one may not clear until another is clear , and each make and model can be different . N.Y. allows one monitor up , 2 in older vehicles and some states will "sniff " your exhaust to make sure that too is O.k. . I guess that all I knmow about codes .