Why should you not use the trailer hand valve to straighten out a jackknifing trailer?

Because the brakes on the trailer wheels caused the skid in the first place.. Section 6.1: If the trailer is skidding, the wheels have lost

Why should you not use the trailer hand valve to straighten out a jackknifing trailer?

ANSWER BREAKDOWN
  • A. Incorrect. "It doesn't work." is not correct. If the trailer is skidding, the wheels have lost traction. Using the hand valve applies more braking, which makes the skid worse.
  • B. Incorrect. "It is illegal." is not correct. If the trailer is skidding, the wheels have lost traction. Using the hand valve applies more braking, which makes the skid worse.
  • C. Correct. If the trailer is skidding, the wheels have lost traction. Using the hand valve applies more braking, which makes the skid worse.
  • D. Incorrect. "It will stall the engine." is not correct. If the trailer is skidding, the wheels have lost traction. Using the hand valve applies more braking, which makes the skid worse.