CDL General Knowledge TestDriving SafelyMedium
A commercial driver notices that their vehicle's dashboard air gauge shows a continuous, gradual drop in air pressure while the engine is running and the brakes are not applied. What is the most likely cause of this issue?
- AA faulty air compressor governor, failing to cut out at the correct pressure.
- BAn over-adjusted slack adjuster, causing the brakes to drag.
- CA leak in the air brake system, such as a loose fitting or a damaged air line.
- DContamination in the air dryer, preventing proper moisture removal.
Show answer & explanationAnswer & explanation
Correct answer: C. A leak in the air brake system, such as a loose fitting or a damaged air line.
A continuous, gradual drop in air pressure with the engine running and brakes off indicates a leak in the air brake system. The air compressor should compensate for normal usage, so a persistent drop points to air escaping the system.
Why the other options are wrong
- A. A faulty governor would affect the compressor's cut-in/cut-out, not cause a continuous pressure drop while running.
- B. Over-adjusted slack adjusters cause brakes to drag and overheat, but not a continuous air pressure drop when not braking.
- D. Contamination in the air dryer affects moisture removal and can lead to air system component damage, but doesn't directly cause a continuous pressure drop.
Air Brake System Leaks
Any unintended escape of compressed air from the air brake system, often indicated by a continuous pressure drop on the dashboard gauge, hissing sounds, or requiring the compressor to run excessively.
- Can be caused by loose fittings, damaged air lines, or faulty components.
- Reduces braking effectiveness and can lead to brake failure.
- Requires immediate attention and repair.
Memory trick: Leaky lines lead to low air levels, needing immediate intervention.