How do you replace or repair a horn? How expensive are they?
The horn tyoically is bolted to the radiator support wall with a single wire plugged into it. Some vehicles have two horns of different tones. You can buy a generic replacement for typically less than $25 at the parts store. Replacement involves unplugging and unbolting the old horn and boting and plugging in the new horn.
Horns will sometimes fail because the bolt that holds it to the wall is corroded. That mounting is the circuit’s ground as well as it’s mechanical mounting, and of there’s too much corrosion it can break the circuit.
Getting to the horn in many new cars is terrible, simply because so many things have to be removed to get access. I’ve never changed one in a Volvo, so the only thing I can offer is my hope that it isn’t too inaccessable.
Only thing would add is: Some times a wire may chafe and render a horn inoperable. You should run a jumper wire to it and see if it works then, if not replace the horn, if so start tracing wires looking for a fault.
Also, many cars use a relay. Have you checked the fuse? Are you sure the horn doesn’t work. and it is not a wiring or relay issue?