Some DCC accessories especially those made by European manufacturers such as Roco, Hornby or Lenz might need additional accessory packets sent before they will respond to accessory commands correctly. To resolve this:
press prog/esc 4 or 5 times to get to "set cmd station".
press enter 4 times - look for "# of ACC Packets" the default is 4
You might need to increase the number of horn stop packets from the default of 4 to a value of 8,16 or 32 try that.
press prog/esc to exit until you see the regular loco screen.