The following are known Action Replay Codes for Gadget Racers on Nintendo Game Boy Advance (GBA).
These codes were also known as GameShark Codes and in most cases will work on both devices.

These codes are for the U.S. version of the game.

Master Code – Must Be On
c2ebdef5
f9bfd32c
cc60cca7
71bc93be

Low Lap Time
d342b339
9d1efa1e
2564b0c1
a9f78e0c
74b15455
01015efa
c76a965a
5721aa0a

Max Cash
7482c234
f3cb8337
4930ae73
1674c0ed