The air pressure to the air horn valve is improper.

Check the operation of the pressure protection valve. Refer to Pressure Protection Valve Operational Check .

There is no air pressure to the air horn valve .

Check all air lines for kinks or other types of restrictions.

The air horn valve is faulty.

The air horn is serviced only as a complete assembly. Replace the air horn. Refer to Air Horn Replacement .

Foreign objects are caught in horn.

Remove the objects.