The following are known Action Replay Codes for Scooby-Doo 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
ac4945b2
bb781cb4
6e3f8e16
8fe19f23

Press Pause for Health / Stamina
e49bc115
6c31c261
b828bde9
23c162da

Max / Infinite Tokens
59a61e88
34a4c64b

Have Tons of Items
e2dbadf3
26dfa988
ad5a2956
624227d8
10a9e6f0
f44aaac4