1998 cadillac deville w/ northstar

I live in new york where you have to have emissions test done. My service light came on and it will not pass with it on. I was told it is for the transmission and they said it will be like 2000 to repair, however, they shut the light off for me and said drive around a bit so 4 codes come back before the light comes back on, this way, it will pass.. Well been trying to do that for sometime and cant time it right for the 4th code to come up before the light comes on. Please does anyone have a suggestion?