Practice question

Before driving a vehicle with air brakes, you should ensure that the spring brakes come on automatically when:

  1. Air pressure falls below 45 psi.
  2. Air pressure falls below 20 psi.
  3. Driving downhill.
  4. Driving uphill.

Answer: A — Air pressure falls below 45 psi.

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Practice more: Pennsylvania CDL Class B Knowledge Test 2 →