You can not unlock it with a cheat code. You will learn it in the fourth year.
On Lego Harry Potter Years 1-4 wii It's in the Leaky Cauldron beside the stairs. You have to use reducto on the lock.
Learn Reducto in the 3rd Year
You unlock reducto in year 4 in defence against the dark arts. Reducto is used for breaking the shiny silver locks and knights.
If it is the DS game, then use the stylus to draw a circle around the character.
There is no tube on Lego Harry Potter.
Use reducto
I think it is either Expelliarmus or Reducto.
On Lego Harry Potter Years 1-4 wii It's in the Leaky Cauldron beside the stairs. You have to use reducto on the lock.
Learn Reducto in the 3rd Year
Use reducto on Dementor's kiss.
You unlock reducto in year 4 in defence against the dark arts. Reducto is used for breaking the shiny silver locks and knights.
Go into Knockturn alley by using the reducto spell on the metal gate. There are also other characters there.
If it is the DS game, then use the stylus to draw a circle around the character.
There is no tube on Lego Harry Potter.
When you are by the vaults at the end of the level, there should be a chest with a lock on it. You have to use reducto to get rid of the lock at the goblin is in there. You have to use free play or it won't work.
I think you go to Knockturn alley (assuming you have reducto) and do something there.
There are about 55 Lego Harry Potter sets to buy.