When starting the electrical diagnosis, first look at the 
Fuses. Pull out the horn electrical connector terminal by unscrewing it from the horn. To check on this, jump the battery voltage to the horn terminal; if the horn does not work, replace it. If the horn does not sound, check for - volts at the terminal when the horn button is depressed. After detecting voltage at the terminal one should look for a bad ground at the horn. In case there is no voltage at horn, check the 
Relay is at the back of the horn. If the above relay is okay, we verify presence of voltage to the relay power and control circuits; if either of the two is missing, then check the wiring at the relay side of the fuse panel. If both relay circuits are getting power, step on the horn button and probe the circuit from the relay to the horn button for continuity to ground. If no continuity is present, measure for an open circuit, if no open is found replace the horn button. If continuity is established to ground through the horn push button, look for an open/short in the circuit from the relay to the horn unit. Horns on models produced from 2001 to 2006 are located at the front of the condenser and are part of the hood latch assembly, meaning the hood has to be opened in order to get to them. For the models produced from 2006.5 and onwards, horn is behind the bumper cover and thus, the bumper cover has to be removed. Remove the electrical connector, then unfasten the bracket bolt, and installation is the reverse of this process.