Question 111 of 140

During the pre-trip check, why is it important to confirm both the tractor protection valve and trailer air supply valve work correctly?

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They ensure the trailer brakes apply automatically if the air supply between tractor and trailer is lost
They are used only when parking on a hill
They regulate fuel flow to the engine
They control only the trailer's interior dome lighting, not any part of the braking system itself

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Correct answer to question 111 (Air Brakes): They ensure the trailer brakes apply automatically if the air supply between tractor and trailer is lost

Why

These valves are designed to automatically apply the trailer brakes if the air supply is lost between the tractor and trailer, such as from a broken line, so confirming they work is a key safety check.

Updated: November 2026

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During the pre-trip check, why is it important to confirm both the tractor protection valve and trailer air supply valve work correctly?

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