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Cheat sheet
Question
Test the tractor protection valve by:
Answers
A.  Removing the air supply knob.
B.  Removing the parking brake control knob.
C.  Releasing air with the brake pedal.
D.  Releasing air with the gas pedal.
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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