Mario Kart DS Cheats help

[the_smudge]

Hey, I come across a lot of peeps who use cheat codes and wanted to at least figure out how it's done.

I have all the cheat codes in my flash cart and have enabled one of them. I can use it in the single player in the game (press X to get red shell), but when I go on the wifi, the X doesn't work to get the item. How do people get those cheats to work not only in single player Mario Kart DS but also on Wifi?

Thanks