It could be a number of things. Check the fuse,then use a test light and touch it to the contacts on the horn under the hood while someone blows the horn. If it lights up its the horn itself. If no light it could be the horn relay in the fuse box or the part you push on the steering wheel. usually it's the relay or a loose wire.
or not listen to someone who knows nothing about your problem. the horn has power at all times and operates by the circuit creating a ground. if you don't know i suggest you don't touch.New HeadlineFor 2003 Sunfire the problem was isolated to the horn pad. Best to disable airbag when working in this area. My horn pad came off by using a screw driver to move aside a shiny metal wire in each of four holes on the back of the steering wheel. Look with a mirror and you'll see the holes and the spring retainer (wire). The pad pushes back in place when and re-engages the retainers when the job is done. There is a wire on a male plastic connector that quarter-twist fits into a female socket on the steering wheel. This wire close the circuit when the pad is pressed. In my case the socket had cracked. My fix was to use a little glue. It works (last 6 mos) but may not be the best solution. The other option, if the dealer understood my need, and I'm pretty sure he did, was to replace the broken part. I was informed by the Ponitac deaer (as I understood him) that the part is integral to the column. Because of liability with respect to airbag, the whole steering column needed to be replaced; part cost $1000.00. Glue seemed like an ok idea.