There was someone on here recently with a gen4 model with the same problem. Before you go diving into the belly of the beast, take a voltage reading on the wire(s) going to the horn(s). He had 12 volts there. He bought 2 new horns and he was back in business. I had an old 91 Camry, bought a relay and chased fuses and what not. I checked the voltage at the horns and it was there. New horns solved the problem
Always make sure you have voltage where you need it, work backwards from there if you don't.