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Cheat sheet
Question
A driver should test the tractor protection valve by:
Answers
A.  Pulling the yellow, diamond-shaped knob.
B.  Releasing air with the brake pedal.
C.  Unlocking the trailer doors.
Explanation
You should test the tractor protection valve by allowing the air supply to properly charge, turning off the engine, then releasing air from the system by pressing the brake pedal several times. The tractor protection valve should move into its emergency position when psi drops to an unsafe level.

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