Remove the front bumper.
Disconnect the 1P connector (A) from each horn (B).
Test the horn by momentarily connecting battery power to the terminal (A) and grounding the bracket (B). The horn should sound.
If it fails to sound, replace it.
Install the horn in the reverse order of removal.
Honda Odyssey Service Manual > HondaVAC™ System Description: Sound Pattern of the Buzzer Pattern 1 ONOFF120±12 ms880±88 ms1000±100 ms Pattern 2 OFFON3000±300 ms ...