The device itself could be bad, or have a blown fuse
This happened to me with my '98 malibu. It was a faulty circuit board, a common problem in malibu's.
What would make your speed odometer stop working after putting an alternator on? 2005 Chevy Malibu
Check fuse,bulbs, flasher
If the gas gauge stops working is there a fuse for it?
In all probability the alternator is not working as it should.
On the 2004 it is in the trunk on the Drivers side.
check heater fan to see if it is working.
check the horn relay or the horn itself!
Replace the battery in the remote
Check the fuse
I have a 2005 chevy malibu and had the same issue... It's the fuel sensor.. Need to replace fuel system
When parts of a car stop working it is important to know the location of its fuse. The horn fuse on a 1999 Malibu is located in the fuse box under the hood.