Practice question

In a dual-line pneumatic brake system, what is the function of the yellow coupling line (Bremsleitung / Steuerleitung)?

It permanently supplies compressed air to inflate the trailer tyres
It is an emergency fuel line supplying diesel to the trailer axle
It provides electrical earth grounding for the trailer chassis
It transmits the variable control pressure modulated by the tractor foot brake valve to activate the trailer service brakes proportionally

Answer: D — It transmits the variable control pressure modulated by the tractor foot brake valve to activate the trailer service brakes proportionally

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