ELDT - Entry Level Driver Training Entry Level Driver Training Vehicle Systems and Malfunctions 1 — Questions and Answers
Question 1: What is the purpose of the tractor protection valve in an air brake system?
- To increase air pressure to the front brakes during hard stops
- To automatically close and protect the tractor's air supply if the trailer breaks away or develops a major leak (Correct answer)
- To regulate the balance of braking force between steer and drive axles
- To prevent the parking brakes from releasing until sufficient air pressure builds up
Correct answer: To automatically close and protect the tractor's air supply if the trailer breaks away or develops a major leak
The tractor protection valve closes automatically when air pressure drops to a critical level (typically 20–45 psi), isolating the tractor's air supply from the trailer to keep the tractor's brakes functional if the trailer separates or suffers a catastrophic air loss.
Question 2: Which of the following is the correct action when you notice your vehicle pulling to one side during brake application?
- Increase brake application pressure to compensate for the pull
- Continue driving at reduced speed and monitor the condition
- Pull off the road safely, inspect for a brake adjustment or mechanical issue, and have it repaired before continuing (Correct answer)
- Pump the brakes rapidly to equalize braking force
Correct answer: Pull off the road safely, inspect for a brake adjustment or mechanical issue, and have it repaired before continuing
Pulling to one side during braking indicates uneven brake adjustment, a dragging brake, or a mechanical defect on one side. This is a safety hazard that must be diagnosed and corrected before operating the vehicle further, as it can cause loss of directional control.
Question 3: What does a continuous or repeated activation of the ABS (Anti-lock Braking System) warning light while driving indicate?
- The ABS is actively preventing wheel lockup, which is normal operation
- A fault has been detected in the ABS system that requires inspection and service (Correct answer)
- The brake fluid level is low and needs to be topped off immediately
- The system is in its self-test cycle and will reset after a few minutes
Correct answer: A fault has been detected in the ABS system that requires inspection and service
The ABS warning light illuminates briefly at startup for a self-test, but if it stays on or reactivates while driving, it signals a detected fault in the ABS system. The base brakes still function, but the anti-lock feature may be disabled, requiring prompt inspection.
Question 4: What is the primary danger of a tire blowout on a front steer axle of a CMV?
- Increased stopping distance due to reduced braking surface
- Sudden loss of directional control that can cause the vehicle to veer sharply (Correct answer)
- Overheating of the adjacent brake drum on that axle
- Damage to the rim that could result in the spare tire becoming unusable
Correct answer: Sudden loss of directional control that can cause the vehicle to veer sharply
A front steer axle blowout is particularly dangerous because steering input is transmitted directly through the front tires. A sudden loss of air causes immediate loss of steering control, requiring the driver to firmly grip the wheel, avoid sudden braking, and gradually slow the vehicle to a safe stop.
Question 5: If you notice steam or smoke coming from the wheel area of your vehicle while driving, what is the most likely cause and appropriate action?
- A loose hubcap rattling against the brake drum; continue to your destination and tighten it
- A dragging or overheated brake; pull off safely, allow it to cool, and inspect before continuing (Correct answer)
- Normal condensation from air brake chambers releasing; no action needed
- An oil leak from the differential; add oil and continue at reduced speed
Correct answer: A dragging or overheated brake; pull off safely, allow it to cool, and inspect before continuing
Steam or smoke from the wheel area is a strong indicator of a dragging brake or severely overheated brake drum. Continuing to drive risks brake failure, fire, or structural damage to the wheel end. The driver must stop safely, allow cooling, and inspect before proceeding.
Question 6: What should a CMV driver do if the oil pressure warning light illuminates while driving on the highway?
- Shift to a lower gear to reduce engine load and continue to the next exit
- Add a quart of oil through the cab-mounted fill port and monitor the gauge
- Safely reduce speed, activate hazard lights, pull off the road, and shut down the engine as quickly as safely possible (Correct answer)
- Increase engine RPM briefly to build pressure, then monitor for improvement
Correct answer: Safely reduce speed, activate hazard lights, pull off the road, and shut down the engine as quickly as safely possible
A low oil pressure warning indicates insufficient lubrication reaching engine components. Continued operation can cause catastrophic and irreversible engine damage within seconds to minutes. The driver must get off the road and shut the engine down promptly to prevent engine destruction.
ELDT - Entry Level Driver Training Entry Level Driver Training Vehicle Systems and Malfunctions 1
What is the purpose of the tractor protection valve in an air brake system?