The flasher unit in a 2004 Chevy Malibu Classic is typically located
under the dashboard, on the driver's side. However, it's not always in the same exact spot and might be slightly different depending on trim level. It's usually part of a larger fuse box or relay center. You'll likely need to remove a panel or two to access it.
It's best to consult a repair manual specific to your 2004 Chevy Malibu Classic to get the precise location and avoid accidentally damaging anything during your search. A visual diagram in the manual will greatly assist you.