Hi who ever sees this.

I got my 99 galant about a year or 1 1/2 ago (it just reached about 90k this wed), and needless to say overall besides me doin some body work due to snow, everythings been ok. Now I dont know much about cars, so if u do reply to this, plz understand im just beginin and may be a lil lost. Now 2 weeks ago when puttin on a replacement hood, the day before i noticed my check engine light came on. To calm my nerves and basically take it off my mind, we just dis connected the battery and boom everything was ok. Well at least till this morn. The light came back on so i went to an autozone to see what code they could come up with. They showed me Warm-Up Catalyst Efficiency below threshold (Bank 1) P0421. Now ive been tryin to search this out and so far i understand it goes with the air flow...but my ? is what do i do to fix this! I commute practically everyday and im still fixin my car from an accident that pretty much only touched the body....so i dont wanna waste money on something i dont need to. If you have any ideas or answers plz reply here or email me at PoconosKel@hotmail.com Thanks in advance!