43. Your emergency air line breaks or gets pulled apart while you are driving. The loss of pressure will cause the:
Detailed Explanation
The correct answer is "Emergency trailer brakes to come on.". This question tests combination vehicles knowledge and the safest action expected of a commercial driver. For a differently worded version of this question, identify the hazard first and then choose the answer that preserves control, visibility, or legal compliance.
Correct Answer: Emergency trailer brakes to come on.
Why This Matters on the CDL Test
This question belongs in your brake safety review. Pay close attention to pressure limits, inspection steps, stopping distance, and warning signs because brake-system mistakes are a common reason CDL applicants miss endorsement questions.
How to Remember It
Say the rule in your own words, then explain why the wrong answers are unsafe or incomplete. That habit makes similar Combination Vehicles questions easier when the exam changes the wording.
Answer Review
Choose "Emergency trailer brakes to come on." because this answer matches the safe CDL action for brake system safety. On the knowledge test, the safest answer is usually the one that protects space, control, visibility, legal compliance, or inspection accuracy before the vehicle is put at risk.
Why the other answers are weaker
- Air compressor to unload instead of pumping air."Air compressor to unload instead of pumping air." does not best answer this brake system safety question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
- Trailer supply valve to open."Trailer supply valve to open." does not best answer this brake system safety question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
Test-Day Checklist
- Read the question once for the topic, then read it again for the exact CDL action being tested in Combination Vehicles.
- Eliminate answers that sound convenient but skip an inspection, warning sign, or safety step.
- Say the correct rule out loud before moving on so you can recognize it when the exam changes the wording.
Ready to practice for real?
Take our free, full-length Combination Vehicles practice test. Simulates the actual DMV exam with timed questions.
Start Practice TestRelated Questions
12. If the service air line comes apart while you are driving a combination vehicle but the emergency line stays together, what will happen right away?
28. You are driving a combination vehicle when the trailer breaks away, pulling apart both air lines. You would expect the trailer brakes to come on and:
38. If the service line comes apart while you are driving a combination vehicle but the emergency line stays together, what will happen right away?
18. You have a major leak in the service line and you put on the brakes. Service air pressure will escape and cause the:
14. In normal driving, some drivers use the hand valve before applying the brake pedal to prevent a jackknife. Which of these statements is true?
Keep Studying Combination Vehicles
Question pages help you review one rule at a time. To build test-day speed, move back into the full Combination Vehicles practice test and answer a mixed set without looking at the explanation first.
State CDL Practice Paths
After you understand this answer, use a state practice path to connect the federal CDL rule with the DMV test pages drivers search for most.