Air Brakes · Question #98

How can you tell if your dual brake system has a leak in one circuit?

A. Low-air warning activates and one system loses pressure
B. Compressor stops
C. Engine knocks
D. Trailer brakes lock

Correct answer: A. Low-air warning activates and one system loses pressure
Explanation: Each circuit has its own gauge; one will fall.

Why this question matters on the Air Brakes exam

This question is one of the 65 we have for the Air Brakes CDL knowledge test. The official AAMVA Commercial Driver License Manual chapter on Air Brakes covers exactly this topic, and most state DMV exams pull from the same chapter. Memorizing the right answer is fine for passing, but understanding the underlying rule is what keeps you safe on the road and out of trouble with FMCSA inspectors.

If this topic gave you trouble, take the full Air Brakes practice test to drill it across all the related questions. We recommend reading every explanation, even on the questions you got right, because the manual phrasing in the explanation often shows up word-for-word on the real exam.

Take the full Air Brakes practice test →