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Combination Vehicles Practice Question 57

Required for Class ACombination Vehicles · Question 57

A pressure test of trailer air lines should include:

• AA leak-down check after charging the trailer
• BVisual checks of glad hand seals
• CListening for leaks at couplings
• DAll of these

Correct answer: D. All of these

Why: A complete trailer brake check includes leak-down, visual seal inspection, and listening for leaks. Any of these can identify problems before the road catches them.

How this question fits the Combination test

Articulated vehicles fail in unique ways: trailer swing under braking, rearward amplification under steering, and jackknife under loss of traction. Combination Vehicle knowledge is required for any Class A applicant under 49 CFR 383.111.

Study technique for this topic

Walk through the coupling sequence verbally until it's second nature. Know the safe-rolling rearward amplification factor, the difference between trailer service brakes and parking brakes, and what creates the conditions for a tractor jackknife.

Related Combination practice questions

• Q11. Off-tracking by the trailer means:
• Q24. When backing into a tight spot, you should:
• Q37. The trailer hand valve is sometimes called:
• Q50. The risk of rollover is greatest when:
• Q64. The forward visibility of a tractor's hood and mirrors creates a blind area in front of th…

Continue your CDL preparation

The Combination Vehicles portion of the CDL knowledge exam covers more than this single question. Use this site's full Combination Vehicles bank to drill every topic, then test yourself with one of our state-specific practice sets to confirm you are ready for the actual DMV exam in your state. Always check your state's CDL handbook for any local addenda before the test day.

If you are still building your overall CDL foundation, start with the General Knowledge bank — every CDL applicant must pass it — and then work outward to the endorsements you plan to add.