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Different tech here.
At connector C131 you need to unplug the harness from the radio and probe the red/yellow wire and press the horn and see if you get 12 volts using a 10$ wire probe or a 30$ multimeter both can be purchased at a parts store. If you get voltage then the signal from the steering wheel is getting all the way to the horn and the horn is faulty. If you dont get power then follow the sire diagram to find where signal is lost from the switch to the horn. The connector and horn is at the the front passenger side of the engine compartment.