Vehicle Inspection
This domain tests whether you can perform and explain a pre-trip inspection, recognize out-of-service defects, and complete required brake checks. The exam asks for sequence, defect thresholds, and documentation-not just part names.
The inspection sequence
Use the seven-step routine: paperwork, engine compartment, cab checks, lights, walk-around, signal lights, brake tests. Inspect tires, wheels, rims, hoses, belts, steering, suspension, coupling devices, and emergency equipment. Know the tire tread minimums: 4/32 inch on the steer axle and 2/32 inch on all other tires.
Air brake checks
The vehicle must be fully charged and the engine off. With brakes released, leakage should not exceed 3 psi per minute on a single vehicle or 4 psi per minute on a combination. The applied leak test uses the same limits. The low-pressure warning must activate before pressure drops below 60 psi, and spring brakes should apply between 20 and 45 psi. The compressor should build from 85 to 100 psi within 45 seconds.
Worked example
A tractor-trailer loses 5 psi in one minute with the brakes released. The limit is 4 psi for a combination vehicle, so the unit fails the static leak test and should not be dispatched. If it lost 4 psi, it is at the limit; a leak that is growing or not stabilizing still warrants service. Read the question carefully: 3 psi is the single-vehicle limit, not the combination limit.
Traps that cost marks
Memorizing one leak number for every vehicle; skipping the applied leak test; assuming lights work without checking them; failing to test the parking brake; and treating a warning at 55 psi as a failure when the rule only requires warning before 60 psi. Also remember that a daily written inspection report and defect certification are required.