What must you do before detaching a semitrailer?

The combination of actions you selected outlines the necessary steps to safely detach a semitrailer from a truck tractor, which is critical for ensuring safety and compliance with German traffic regulations.

1. Locking the wheels of the semitrailer and extending the supporting legs prevents the semitrailer from rolling or tipping over during the detachment process, maintaining stability.

2. Disconnecting all hose and cable connectors is essential to ensure that the air brake system and electrical connections are safely disengaged, which prevents any accidental engagement of the brakes or electrical circuits while the semitrailer is being detached.

3. Releasing the coupling lock and opening the hitching device of the fifth wheel is the final step that allows the semitrailer to be completely separated from the truck tractor without damaging the coupling mechanism.

Following these steps not only ensures that the semitrailer is safely detached but also adheres to the safety protocols established in German traffic laws. Each action is interconnected and vital for a safe and successful detachment.