Most Common Pre-Trip Inspection Failures
The CDL pre-trip inspection test requires the candidate to demonstrate knowledge of every major vehicle system and explain what they are looking for and what constitutes an out-of-service condition. Examiners score the inspection by component area — the candidate must correctly identify and describe each item in each area. Missing items within a component area results in point deductions, and missing entire component areas results in larger deductions.
The most frequently failed pre-trip inspection component areas on the CDL skills test are: the engine compartment (candidates often skip certain belts, hoses, or reservoirs because they are not visible without leaning into the compartment), the air brake system (candidates describe the visual components correctly but fail to state specific out-of-service criteria such as the 3 psi per minute leakage standard), lighting (candidates demonstrate activation of lights but fail to check all lamps including clearance lights, marker lights, and reflectors), and coupling inspection (candidates check the fifth wheel but fail to demonstrate the tug test or fail to check safety items like glad hands, security of trailer plug, and trailer tandem pin condition).
For the air brake inspection, the candidate must demonstrate both the visual inspection (checking all four brake chambers, all brake lines and hoses for damage, all slack adjusters for adjustment and condition) and the operational checks (building air to governor cutout, testing low-air warning, testing emergency spring brakes by allowing pressure to drop to the specified threshold, and the 3 psi per minute static air loss rate test). Many candidates know the visual inspection but rush through or omit the operational checks, which are heavily weighted in the scoring.
The tire inspection is another frequent failure point. Candidates must demonstrate knowledge of minimum tread depth (4/32-inch for steer axles, 2/32-inch for all other positions), proper inflation indicators (valve stem caps, visible inflation gauge, absence of bulges or cracks), and out-of-service conditions (re-grooved tires on steer axle, recaps on steer axle). Rushing through the tire inspection and using vague statements like 'tires look okay' will result in deductions — specific tread depth minimums must be stated.