What will be the effect if the brake line hose with the yellow coupling head tears between the towing vehicle and trailer during braking?

When the brake line hose with the yellow coupling head tears between the towing vehicle and trailer, safety mechanisms activate to prevent loss of braking control. The four-way protection valve ensures that the towing vehicle’s service brake system maintains enough pressure, so your vehicle remains safely braked. At the same time, the trailer’s supply line is automatically vented (air escapes), which causes the trailer brakes to engage, slowing or stopping the trailer independently. This design prevents the trailer from going unbraked and maintains overall safety. The trailer’s service brake system does not fail; instead, it is activated as a safety response. This combined effect protects both the towing vehicle and trailer during an emergency situation.