CDL General Knowledge TestAir Brakes (if applicable)Medium
A driver notices that the air compressor cycles on and off more frequently than usual. During a pre-trip inspection, they find that the air pressure in the primary tank drops from 125 psi to 100 psi in 3 minutes with the engine off and the brakes applied. Which of the following is the most likely cause of this issue?
- AA faulty low air pressure warning light sensor.
- BA misadjusted slack adjuster on a service brake.
- CA clogged air dryer filter.
- DExcessive air leakage in the brake system.
Show answer & explanationAnswer & explanation
Correct answer: D. Excessive air leakage in the brake system.
A significant drop in air pressure over a short period with the engine off and brakes applied indicates excessive air leakage within the air brake system, forcing the compressor to work harder.
Why the other options are wrong
- A. A faulty sensor would affect the warning light, not the actual pressure drop rate.
- B. A misadjusted slack adjuster affects braking effectiveness, not the rate of air pressure loss when the engine is off.
- C. A clogged air dryer filter would primarily affect the removal of moisture, not directly cause rapid air pressure loss or frequent compressor cycling due to leaks.
Air Brake System Leakage Test
A procedure to check for excessive air leaks in a commercial vehicle's air brake system, crucial for safe operation.
- Vehicle off, brakes applied.
- Pressure drop should not exceed specific limits (e.g., 3 psi in 1 minute for single units, 4 psi for combination units).
- Excessive drop indicates a leak needing repair.
Memory trick: Leaky Brakes = Frequent Compressor Calls