Vehicle Inspection
What the exam tests
Vehicle inspection questions ask you to find defects before a trip and to know which defects make a vehicle unsafe. The Pennsylvania CDL General Knowledge test draws on the pre-trip inspection you must perform and the conditions that put a vehicle out of service.
The inspection sequence
- Walk around the vehicle before driving: lights, tires, wheels, brakes, body, coupling, and load securement.
- Check the engine compartment for fluid levels, belts, hoses, and leaks.
- In the cab, test gauges, warning lights, horn, wipers, mirrors, and seat belt.
- Test the brake system, including air pressure buildup and leakage on air-brake vehicles.
- Check tire tread: at least 4/32 inch on front steer tires and 2/32 inch on other tires.
Worked example
A driver finds a front steer tire with 3/32 inch tread. Is the vehicle legal? No. The steer-axle minimum is 4/32 inch, so the tire must be replaced before dispatch even though 3/32 inch would pass on a rear tire. The reasoning is axle-specific: steer tires carry steering and braking loads and have a deeper minimum.
Traps that cost marks
- Treating the pre-trip as a quick glance; exam questions reward a systematic sequence.
- Confusing the 4/32-inch steer minimum with the 2/32-inch general minimum.
- Ignoring an air leak because the gauge looks fine.
- Forgetting load securement and coupling checks, which are part of the inspection.
Exam tip
If a question asks what to do when a defect is found, the answer is usually to correct it or place the vehicle out of service before driving.