Vehicle Inspection
Vehicle inspection is where the Maine CDL general-knowledge exam checks whether you can find defects before they become crashes. Expect questions on the seven-step pre-trip, the air-brake tests that belong to it, tire and brake standards, and what makes a vehicle out of service.
The seven-step sequence
The federally derived sequence is: (1) vehicle overview, (2) engine compartment, (3) cab check and engine start, (4) walk-around front, (5) sides, (6) rear, (7) brake check. The order matters because you start the engine only after checking fluid leaks and belts, and you test brakes last, with air pressure built up.
What to reject
Look for puddles and fresh drips, cracked or glazed belts, frayed wiring, cracked drums, missing lug nuts, and tire damage. Minimum tread is 4/32 inch on steer tires and 2/32 inch elsewhere; check for cuts, bulges, and exposed cord. Every light must work, including clearance and marker lamps. Emergency equipment - extinguisher, warning triangles, spare fuses - must be aboard.
Worked example
You charge the system to 120 psi, shut the engine off, and watch the gauge for one minute. It falls to 117 psi. On a single-unit truck the allowable loss is 3 psi per minute, so 3 psi passes. The same 3 psi loss on a combination vehicle also passes, because its limit is 4 psi. A 4 psi loss on the single unit would fail. Reasoning: the test is a leak rate, not a pressure target, and the limit depends on vehicle type.
Traps
Skipping the engine-off leak test; assuming a slack adjuster is fine because it moves; inspecting the tractor but not the coupled trailer; and writing up a defect without understanding that an air leak can cause a weak or dragging brake.